Sounds like Opera is crashing and then corrupting your profile data because it's not being shut down properly.

You should probably uninstall and reinstall Opera, and start with a new profile to make sure nothing is corrupted. Then, test without logging into Opera Sync for a bit to make sure it's not Sync that's causing Opera to crash.

If you think it's Sync that's causing Opera to crash, you might want to wipe out your data on the Sync server by going to https://www.sync.opera.com/ and choosing "Reset passphrase". Then, start with a new Opera profile again.

If you can get a crash ID and post it here, that might help too.