Suddenly the automatic cloud sync on exit stopped working. Manual sync works fine. I'm using Quicken Classic Premier for Windows. This has happened before, and I believe the solution was to delete and recreate the cloud data. I just found a simpler and less invasive answer in this post:
Auto Sync on Close doesn't start automatically — Quicken
The solution there was to log out and back into the Quicken account. Worked for me too.