The issue was resolved with QuickBooks tier-2 support over the phone with screenshare.

It wasn't the company file size. It wasn't a Verify Data issue. Tier-2 support checked all that. But thank you for the suggestions.

Instead of pushing the Data Migration from QB Desktop to QB Online, tier-2 support had me export the company file to a backup QBB file on my PC. Then we went to the QBO initial setup and uploaded the QBB file from my PC to the cloud folder (QBO is on Amazon AWS). Then we migrated the file on the cloud folder to QBO. That worked.