Since the last major update to 2.0, it has gotten immensely better. Whereas before the app was hung for 30 seconds on startup and would only reliably sync in the foreground for my partner, it now just works. Can open, syncs in the background. Never had such issues on my phone, probably the size of your collection matters here.

Does it recover though, or do you end up in situations where your setup is essentially broken?

Like if I backup photos from iOS, then remove a subset of those from iOS to make space on the phone (but obviously I want to keep them on the cloud), and later the mobile app gets out of sync, I don't want to end up in a situation where some photos are on iOS, some on the cloud, but none of the devices has everything, and I have no easy way to resync them.