I know this has been an issue for a while. There are posts here and on Reddit about this happening, and I already ran through the fixes they suggested.
I was in a chat with support at Quicken, and they had me run through all the steps to try and fix the problem, but nothing worked. Then they abruptly ended the chat, just saying, Quicken is aware of the problem with Capital One and is working on it. That was a couple of weeks ago.
I can't even deactivate the account and import QFX from the bank.
[Edited - Readability]