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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TaoLi 113.9K Reputation points Independent Advisor

2026-09-21T15:20:14.1733333+00:00

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.
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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/
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IE compatibility mode not working since recent Windows updates

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