To somewhat echo other comments here: users need to be very careful with the git syncing. It works most of the time when edits on git clones and edits on the web interface are being made at very separate times, and when nothing at all is done in git other than committing, pulling, and pushing (if I recall, even signing can break it). But amongst the people I know who have used Overleaf for important projects with collaborators, the git syncing has generally worked reasonably right up until it is needed the most: important, tricky changes; multiple authors meeting online and editing; oncoming deadlines for conference paper submissions resulting in many edits over a short time scale. In critical situations, it can often become unusably slow (potentially tens of minutes, to hours, to get a successful pull or push), or simply fail.

One group with a paid, group subscription asked support about the instability, and was simply told their use case was unusual (writing conference papers with some git and some web editors?). They are now planning on moving away from using it.