Preserve Master Slides is not working in PowerPoint

Interesting problem. Given that you have already tried keeping a slide associated with each preserved master, I would also look at the template architecture itself rather than relying solely on Preserve.

If the eight masters are principally dark/light and security-classification variants of the same core design, I would first check whether some of those variations can be handled through layouts and theme colours beneath fewer masters. Multiple masters are sometimes necessary, but I generally try to minimise them in corporate templates because each master introduces another independent hierarchy of layouts, placeholders and formatting to maintain.

I would also test the template locally as a .potx, outside OneDrive/SharePoint, then close and reopen it repeatedly. If the masters remain intact locally but disappear once the file is being synchronised, that gives you a useful distinction between a template-structure issue and a file/synchronisation issue.

I would be interested to know whether the deleted masters are always the same ones, and whether they disappear immediately after reopening or only after further editing.

The AI answer is partly true.

It does not cover the problem that even with:

• Preserve enabled
• Live slide examples from each master in your deck (not Slide Master; Normal view)

...slide Masters will still disappear if you have too many of them. I would add:

• Limit your template to 3 or 4 Master variants.

Thanks for your detailed response, @Caspar Field,.

Based on previous reports from other users, this appears to be an issue that can occur even when Preserve Master is enabled and the master displays the pushpin icon. Similar cases have been discussed in the following Microsoft Q&A threads: Powerpoint Master Templates Disappearing - Microsoft Q&A

Notably, in the discussion, PowerPoint MVP and Volunteer Moderator John Korchok acknowledged that he has occasionally encountered presentations where preserved Slide Masters were still removed unexpectedly. His recommendation was to ensure that each Slide Master has at least one slide actively associated with it, as PowerPoint does not remove masters that are in use by existing slides.

Given that the masters removed from your presentation were preserved but not assigned to any slides, the most reliable workaround I can suggest is to maintain a placeholder slide for each master within the template. Many organizations keep these slides in a hidden section or at the end of the presentation to ensure the associated masters remain in use and are retained.

In addition, I would recommend contacting Microsoft Support directly. Since you have experienced actual data loss and invested significant effort in creating the master slides, support can help determine whether this is caused by a known product issue, a template-specific corruption, or an issue related to your Microsoft 365 build.

For business support:   

• Find your Microsoft 365 admin: If you don't know who the global admin is in your organization, you can find guidance here: How can I find my Microsoft 365 admin? - Microsoft Support    
• Submit a service request: The Global Administrator should create a support request with Microsoft to receive advanced technical assistance. For detailed instructions, see: Get support - Microsoft 365 admin | Microsoft Learn    
• If your subscription is from a partner or reseller, contact the reseller's support provider to help open a service request on behalf of you instead.    

If you discover any solutions or have additional insights, please consider replying to this thread to help others in the community.   

I sincerely apologize for redirecting you to the Microsoft Technical Support Team. While I strive to assist as much as possible here in the forum, my resources are limited when it comes to backend-level diagnostics and advanced troubleshooting. Some issues require deeper technical analysis and access to internal tools that only the official support team can provide.    

If you need further assistance, feel free to reply. I'm here and happy to help!   

Hello @Caspar Field,

Good day! I hope you are doing well.

Based on your description, I understand that you created a PowerPoint template containing six different Slide Masters, enabled Preserve Master for each one (confirmed by the pushpin icon), but after saving, closing, and reopening the file, several of the masters were unexpectedly removed. You are concerned both about recovering the missing masters and preventing the issue from occurring again in the future.

Please let me know if I misunderstood any part of your issue or if there are additional details you'd like to share.

To help us provide the most accurate and effective solution for your issue, could you share a bit more detail about your setup:

• What version and build of PowerPoint are you using? (File > Account > About PowerPoint)
• Does the issue occur consistently every time the file is reopened, or only occasionally?
• Were the deleted Slide Masters actively being used by any slides in the presentation, or were they preserved but not assigned to any slides?
• Additionally, have you ever received a prompt similar to the one below when saving or closing the presentation? If yes, what option did you choose?

• Does the same behavior occur if you save the presentation locally on your computer rather than in OneDrive?

This additional context will help us understand your environment and the steps already taken so we can tailor the guidance to resolve the issue effectively.

Looking forward to your response so we can get this sorted out for you together.

If you have extra questions about this answer, please click "Comment".    

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