Several times in the last few weeks the NDI input vMix is receiving from ProPresenter (current version, we use it for the announcement slides and for song captions) something is happening causing vMix to stop following the NDI input, leaving whatever slide or caption it last received as the display.

We also provide four NDI outputs from vMix that are displayed on various monitors around the church.

We have five cameras, all NDI in addition to the two NDI inputs from ProPresenter. The ONLY NDI inputs locking up are the ones from ProPresenter, one input from ProPresenter is the full slide image for the announcements display, the other is a text only input for song caption overlays during the song service.

Checking with Studio Monitor from NDI Tools shows that the PC running vMix IS getting the slides but somehow vMix is loosing track and disconnecting. This has worked fine for many years and many versions of vMix and ProPresenter and we have been using the current versions of both for many months now, this is a new and unexpected behavior.

The question right now is what sort of issues can cause the vMix input to disconnect and not notice it needs to reconnect?

Something has changed and it wasn't the ProPresenter or vMix software, I need a direction to try to hunt down this problem.

Edit: Windows 11 of course gets changed regularly.

First try in Studio monitor. This is your reference.
Have you tried NDI analytics. You can download it from vizrt. It can show some insights.
Do a wireshark recording while it happens and check where the issue is.