I just had a scary experience today where Q was giving me several error messages and doing some other strange things. I eventually called support and talked to support for 44 minutes. The agent was very pleasant and tried to be helpful, but we did not resolve the problem.
About the first thing he did was have me turn Sync On. (I do not like it on and even less now.) We tried several things including super-validation. Then we tried restoring a file from before this started. (I had zero problems and everything was correct through June 30.) Unfortunately the same error flags appeared as soon as we opened the restored file. This even occurred when I tried a June 4 file. The transactions correctly ended at June 4, kind of indicating I had the correct file, but the error flags were still flying
Why did the restored file from before the problem still have errors? After reading another discussion about similar problems, I thought the problem was the sync — picking up the corruption and syncing back into the previous "good" file. Sure enough, I turned Sync Off and reloaded the backup file with no problem.
I am now operating on the reloaded backup from June 29 and processing the intervening transactions. That seems to be going OK.
For a test, I reconnected the error institutions in the current file. They worked, but the reconnections created bogus final entries which I deleted to get correct balances.
For the record, this is Windows 11, Q 27.1.67.10. The errors were CC-800 for two banks and two credit card companies. My OSU settings were also wiped out and one account name became N/A. (Four other accounts had N/A for a while, but they were corrected by the validation.) The N/A account still has account 3, etc and could even be updated in OSU.
I suggest support revise their protocol to be more careful about going to turn sync on early in the testing process.