Hi Laurie,
Thanks for posting back and sorry for my late reply.
I didn't mean to not reply to you, I only received your Feb 10th reply notification email, but not the Feb 5th reply notification email. I think there is a problem with the community's notification system. As far as I know, some threads were affected, and the notification email may not have been sent.
Regarding Answer 5, if you delete the file and restore it, it will keep the original ID number. In this case, I recommend you delete and then restore the file.
Based on my testing, it works fine with the same library settings. Since you can edit the file in the web app, this means that this situation is not caused by permissions. I would like to know how you open the presentation in the app. Generally, you can click File> Open> select the SharePoint service and then open the presentation, or open it in the web app first, and then click "Editing" in the upper-right corner> Open in Desktop.
If your steps are correct, but the problem still occurs, I would like to know if you have synced this SharePoint library/folder to your device (so that you can see and open the SharePoint file from File Explorer). If you have synced the SharePoint library/folder, I suggest you right-click the file in File Explorer> Properties> under the General tab, make sure that the "Read-only" option unchecked.
In addition, I recommend you download, re-upload, and replace the presentation. See if the problem still occurs.
Go to the online location in the browser, download the presentation to local, create a new blank presentation, click Insert> the down arrow of "New Slide"> Reuse Slides> Browse> select the local presentation> Insert All> save the new presentation with the same name, go to the online location, and click "Upload". If you can replace the original presentation, check to see if the problem still occurs.
If the problem persists, then this is not normal. I have tested and searched a lot. Frustratingly, I didn't find any settings that may cause this behavior. In this case, I think it would be better to check your tenant environment remotely for further troubleshooting. I suggest raising a support ticket from the Microsft 365 admin center, where the related team will investigate the problem further by collecting the necessary background logs. You can contact your tenant admin or IT team and ask them to create a support ticket with Microsoft Support directly by following the steps from this link: Get support - Microsoft 365 admin | Microsoft Learn
Sorry for the inconvenience that happened to you. Appreciate your understanding and patience.
Sincerely,
George | Microsoft Community Moderator