Are you Syncing to Mobile/Web?Do you use the Mobile app on your smartphone or the Quicken on the Web feature?
If no, turn Sync off completely. You don't need it.
If yes, try to Reset Sync so that the current cloud sync file is replaced with a fresh complete copy Do note that a full Sync process may take many minutes to complete.
Log out of your mobile app, then do this on your desktop / laptop:
How to reset Sync to Cloud
How to turn off Sync to Cloud for the current data file