I’ve only posted on this forum once due to hostile replies. However…
I had the same problem.
The phone was finding two routers with a very strong signal, one mine (which is a wired connection) and another from a nearby neighbour. On opening the app, sometimes it connected to my router (so it worked) but usually to the other router so it didn’t work.
It was solved in settings where the neighbours router could be deleted. That was several months ago and no problems since.