EDIT: Although the issue as described still happens to me occasionally, it appears today's instance of the problem is coincidental and instead related to the ongoing BoA issue in another thread.
Short summary: There appear to be some cases where the account name in Quicken is used literally in the online update process, when this should be cosmetic and seen only by me in Quicken.
Verbose: This has happened many times over the years and there is something I can do to make it not an issue anymore, but it isn't clear what that something is. Let's say I add an account with Express Web Connect+ connectivity. It creates an account "CD 123456" in my account list. As long as I leave it as is, I can do updates just fine. But that name being unhelpful, I rename the account to "Acme Bank XX3456 CD". The next time I do an update, I get an error that this account doesn't exist.
This can also happen if I change my password at the institution and for some reason, I have to reset the account. The name that I've been using successfully for months is not found.
The odd thing is that there is a solution to this because eventually I can get an account renamed to my liking and it sticks and updates without issue. I just don't know what that is. I've tried resetting account and disable/enable online services and I can't get past this issue.