There's no unsync anymore, all sending wallets are now always stored encrypted on the server.

The first device you opened SN with today gets to set the key, and when you use a different device, it will either already have the same key, or it won't, then it will ask you for the passphrase to derive the same key.

But I think something went wrong with detecting existing keys, so we accidentally generated new keys for some 🙈

But not sure if your wallets loading forever on mobile is related to that.