Target was having a known issue. I couldn’t log into their website and Tiller wasn’t updating. For me at least, this problem went away yesterday and everything is working again. Don’t know about Capital One.
In general, it’s best to open a ticket with customer support through the chat window on the Tiller Console page for individual connection issues. Hard for any of us to see what might be going on with a particular institution. Fwiw, Cap One has been working just fine for me, so there’s something worth investigating with your account.