I'm on Mac, Quicken Classic Deluxe, version 7.4.2. But this isn't a software issue.
I had a mutual fund account linked to Quicken for years. In September, they had a rule change that required that account to be closed and transferred into a brokerage account, which has a different account number. At the time, I didn't change the download settings to the new account number, so it stopped downloading to the register.
I entered missing transactions by hand for a few months, and just now changed the account number so I could get future downloads. The result is that it all transactions are missing from the register and from all reports,. It's treating it as a new account with the same name and has deleted the old transactions (though, dividends from the old account to a checking account are still there).
I've seen a similar problem with credit cards that are lost/stolen and require new numbers; the recommendation for that is the disconnect/reauthorize routine. But in my case, my old account isn't there to be linked to the new one.
The only fix I can see is to restore a backup with the old account, rename it "Old bank" and start a new one called "New bank". Or am I missing something?