What would cause video to stop playing on server?

Using Presenter 11, I published a module from PPT with several short videos, then moved to our server for linking to an LMS. A few individuals viewed the module and the videos were working fine on the server. A few weeks have passed and the videos no longer play. Sometimes a bar appears that looks like video is downloading, but it quickly disappears and the slide is left blank.

I copied the files back to my desktop and launched---all videos display correctly.

Why would it STOP working on the Server?

I don't have admin ability on my server---but wondering if a missing or additional software update could cause the issue? (But what? I need to have something to add to my helpdesk ticket.)

We are going through waves of Office 365 conversion onsite---are there incompatibilities with that?