IE compatibility mode not working since recent Windows updates

Question

IE compatibility mode not working since recent Windows updates

Shaw, Matthew 10

Since the middle of August my team have faced issues whereby although IE mode is turned on for a specific web app it doesn't appear to be working. All the options are activated, the task bar shows IE mode is on but the calendar on the web app that relies on IE 9 isn't working properly.

I have seen an article in ghacks describing the issue but no official Microsoft confirmation.

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6 answers

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Answer 1

TaoLi 113.8K Independent Advisor

Hi

Since IE mode is already active, I’d first check whether the page is using the IE9 document mode the calendar needs. Click the IE icon beside the address bar and share a screenshot of the compatibility mode shown, hiding any internal website address.

Could you also share your Edge version from edge://settings/help, the Windows update KB number installed around when this started, and the ghacks article link? I can’t confirm a known update issue from the symptoms alone, but those details will help narrow it down.

Shaw, Matthew 10 Reputation points

2026-09-21T15:43:30.8733333+00:00

Version 153.0.4234.32 (Official build) (64-bit)

The KB version is harder to pin down as it is affecting a team of people all getting the update(s) at different days/times - I can see I got 6 KBs on one day, I suspect the most likely being KB5121003

https://www.ghacks.net/2026/08/16/microsoft-confirms-windows-11-bug-breaks-ie-mode-in-microsoft-edge-for-some-users/

Answer 2

TaoLi 113.8K Independent Advisor

Leave the affected page open, press Win + R, and run %systemroot%\system32\f12\IEChooser.exe.

Select the affected tab, open Console, then try using the calendar again.

Share any error shown, hiding internal addresses, along with the Windows version and OS build from winver.

Shaw, Matthew 10 Reputation points

2026-09-21T16:44:03.6033333+00:00

Version 25H2 (OS Build 26200.9168)

These are the errors I repeatedly see, I will ask the team tomorrow to test on a user where it is working vs one that doesn't to see if the errors are different:

DOM7009: Unable to decode image at URL:

SCRIPT438: Object doesn't support property or method 'corner'

SCRIPT16386: No such interface supported

SCRIPT5007: Unable to get property 'parentNode' of undefined or null reference

Answer 3

TaoLi 113.8K Independent Advisor

Hi

Your PC is still on the August Windows build. I suggest asking IT to test cumulative update KB5129195, or a newer approved update, on one affected PC, then restart and try the calendar again.

KB5129195 brings Windows 11 25H2 to build 26200.9457: https://support.microsoft.com/help/5129195

This is a troubleshooting step; Microsoft hasn’t documented it as a fix for these particular errors. If the problem remains, the application owner will need to investigate the first failing script and why the “corner” method is unavailable.

Shaw, Matthew 10 Reputation points

2026-09-22T09:20:49.1833333+00:00
Thanks I'll talk to our IT admins to see if this can be tested, the only other thing I came across was.....

If the affected user logged into the web app on an unaffected users laptop and windows login the issue was resolved.

If the affected user then logged in with their windows/domain account on the unaffected users laptop, the issue returned.

This seemed to suggest a windows profile problem? I had also tried getting the user to generate a new local Edge profile and the problem persisted, again I fear this is just pulling the issue from the global profile?

Do you know if the global profile contains an edge profile that can be cleared?
Shaw, Matthew 10 Reputation points

2026-09-24T12:07:47.5633333+00:00

We have a couple of affected users that now have this patch KB5129195 but are still experiencing the same issues

Answer 4

TaoLi 113.8K Independent Advisor

Edge settings can roam if IT enabled it, but a new Edge profile won’t reset IE mode’s Windows settings.

First, while signed in as the affected user, go to Edge Settings ， Privacy, search, and services ， Clear browsing data ， Clear browsing data for Internet Explorer. Clear only temporary internet files, then restart Edge.

If it persists, ask IT to compare the affected and working users’ policies and Internet Options settings.

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Answer 5

快被烤焦的魚洪 10

We are seeing a similar issue in our environment.

Based on our testing so far, the issue may be related to one or more of the following Windows updates:

KB5120998

KB5120997

KB5122385

We have not yet confirmed which specific update is the root cause.

As a temporary workaround, we downgraded Microsoft Edge to version 151, and IE mode works normally again in our environment.

We are still testing newer Edge/Windows update combinations to determine the exact cause. If anyone has confirmed whether this issue is fixed in Edge 153 or a newer Windows cumulative update, that information would be very helpful.

Shaw, Matthew 10 Reputation points

2026-09-24T08:32:02.8266667+00:00

Amazing thank you, the timing of our issues also point towards a Windows update rolled out in August, however I think I'm on a different OS build to you so the KBs are different, I'm not sure how to compare them. We received:

KB5121003

KB5120708

KB5054156

KB5122105

KB5122106

KB5120710

KB5122104
快被烤焦的魚洪 10 Reputation points

2026-09-24T08:39:08.56+00:00

Thanks for the additional information.

On my side, I’m currently running Windows 11 Pro 25H2, OS Build 26200.9550, so my system is already on a newer Windows build than yours.

The IE mode issue still occurs in my environment with the newer Edge versions. However, after rolling Edge back to version 151, IE mode works normally again.

Because of this, I’m starting to suspect that the issue may not be tied to one specific KB, but rather to a combination of the Windows updates released since August and newer Edge versions.

If possible, could you try temporarily rolling Edge back to version 151 on your 26200.9168 system and see whether IE mode starts working again?

If it does, that would give us a pretty useful A/B comparison:

Windows 25H2 + Edge 153 → issue occurs Windows 25H2 + Edge 151 → works normally

That might help narrow down whether the regression is mainly on the Edge side or related to the interaction between Edge and the Windows IE/MSHTML components.
Shaw, Matthew 10 Reputation points

2026-09-24T09:21:37.4133333+00:00

I'm talking to our IT admin to see if we can try this on a spare laptop, unfortunately that is a slow process here. I can see I am on Edge v 153.0.4234.48 (updated today)
Shaw, Matthew 10 Reputation points

2026-09-30T13:39:05.6166667+00:00

Further update, upon downgrading to Edge v 151 the issue was resolved for us.

What I found is that with v 151 the toggle buttons exist (image from MS Learn page):

Now despite the fact that the page I was on had IE mode activated (IE9 mode), the toggle switch for compatibility mode was in fact off!! so I switched this on and our issues was resolved, I then proceeded to update back to the latest version 154 and although the toggle switch functionality is now removed, our app continued to work with IE mode functioning as expected.

I need to test this now with further test devices before rolling out to those affected. But it appears to be all those that have been with the business longer and used the older edge versions with the toggle switched on before auto upgrading work fine, and all newer starters in the team that seemingly missed applying the toggle switch have issues.
快被烤焦的魚洪 10 Reputation points

2026-09-30T14:42:07.52+00:00

Thank you very much for the detailed follow-up and for taking the time to investigate this further.

This is a very important finding. The fact that Compatibility View was disabled in Edge 151, and that enabling it resolved the issue even after upgrading back to Edge 154, gives us a much clearer direction for further investigation.

Your observation regarding older devices potentially retaining this setting, while newer users or devices may never have had Compatibility View enabled, is particularly valuable. We will reproduce the same sequence on our affected devices by downgrading to Edge 151, enabling Compatibility View, and then upgrading back to Edge 154 to verify whether the behavior is consistent.

Thank you again for sharing the test results and the detailed explanation. This may provide an important clue to the underlying cause of the issue.
快被烤焦的魚洪 10 Reputation points

2026-10-01T05:40:58.11+00:00

These registry settings originated from an internal workaround package provided by our company's Infrastructure team after we encountered a similar Microsoft Edge IE Mode compatibility issue.

After the package was applied, affected users reported that the legacy application worked normally again. We have also confirmed this behavior on Microsoft Edge 154.0.4258.48.

Please note that these registry settings were specifically prepared for our corporate environment. They should not be considered a universal fix, and not every setting will necessarily be required in another environment.

If you are investigating a similar IE Mode compatibility issue, I would recommend reviewing 02_Compatibility_View.reg first, as it contains the Compatibility View / Browser Emulation settings most directly related to the behavior we observed.

The remaining registry files modify pop-up handling, Trusted Sites, cookies, ActiveX, downloads, authentication, and other IE security-zone settings. Some of these settings have security implications, so they should be reviewed with your Infrastructure or Security team before deployment.

Please refer to README_EN.md for the detailed usage instructions and reg.md for the complete consolidated registry configuration.

IE_Mode_Compatibility_Workaround.pdf
Shaw, Matthew 10 Reputation points

2026-10-01T15:33:26.4933333+00:00

Thanks for sharing this, I was able to discover a reg entry to deploy to the affected users that has fixed our issues.

What we identified was that for those that had enabled compatibility view in an earlier release of Edge (v151 or earlier), they had an additional reg key for the IE browser emulation, storing the website url which had persisted despite updating to a later version. By exporting and importing this for affected users the issue was resolved. (Edge v154). Here is the key location:

\HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\BrowserEmulation\ClearableListData\UserFilter