A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
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!