I really have the feeling that it's related to this audio over HTTP (which anyway doesn't seem to work and I doubt worked before).
So first thing here, please disable the audio by removing the checkbox Audio over HTTP for all the cameras that do have it (apart if some do have audio working) and report back if from this point the software is stable.
I couldn't replicate the problem here however i'm already one version further in term of ffmpeg so maybe that's why.
Btw it would be easier to regroup the 2 cases. maybe you can follow-up this thread:
I will report in that one from now since the title is more relevant to the issue I'm looking at.