We have given several staff bluetooth headsets for making calls via teams. The headsets are not dropping out during calls, but between calls Teams is periodically switching the audio device to something else.
I suspect that the bluetooth headset is essentially going to sleep after not being used for a while, and Teams is no longer detecting it, so is switching to a different audio device, but is not switching back when the headset is turned back on.
Frustratingly, the issue is not consistent, as some users seem to have no problem at all, while others have it regularly, and also the users who are effected don't experience it consistently. Sometimes they can go hours between calls and it picks right back up where it left off, other times they might go 10 minutes between calls only to find that it has disconnected again, and the sound is coming out from speakers instead of the headset.
I have only noticed this on a couple of more recent cases, but at least some of the time, it is only the speakers which are changing, Teams is still using the headset microphone. I'm not sure yet whether this is happening every time and I just didn't notice it the first few times, or not.