(8/24/2024) I have the same issue with Quicken downloads that has been report on the community many times. The difference for me today is Discover is locking out my account when I try to reactivate and add a Discover Bank account.
I had to contact Discover web support to get my account unlocked so I could log back into Discover. While I had then on the phone and after they unlocked my account, I tried to reactivate one of my Discover accounts in Quicken and Discover immediately locked me out again and they had to reset my account so I could log back in.
The support person told me it would happen every time I set up a new Discover account or tried reactivate an existing Discover account in Quicken….! They told me the reason it was happening is that Discover is no longer supported in Quicken.
So beware if you are trying to add a Discover account to quicken, Discover may lock you out and you want be able to log in to your online Discover account.