I'm having an identical problem as this user:
https://community.quicken.com/discussion/7969061/unexpected-error-message-q-mac
The first time I try to load my data file, I get an error that an unexpected error occurred, and Quicken needs to quit. Relaunching always seems to open the file without an issue. My file is stored locally on my MacBook.
I've tried uninstalling and reinstalling Quicken. I've tried restoring from a backup. The problem actually went away for a while recently but has started happening again.
It's a nuisance more than anything, but I'm nervous that there's some issue that's going to eventually cause a real problem. What can I do to troubleshoot this?