Kentico 13 Admin screen lock: problem signing back in

When Kentico locks the screen after 20 minutes, it shows a sign in modal but for some reason I can't sign back in with that modal. Nothing happens after I enter the username and password, and the screen remains locked. No error message in the event log or javascript console. The expectation is that the screen is unlocked and I can continue working on the specific page or object.

I'm forced to refresh the admin site, which sends me back to the sign-in page. There, I can sign back in and I am returned to the app I was working in (but not the specific page or object).

I don't know of a setting that would change this behavior. Does anyone know how to fix this? (My hotfix version is 13.0.73). And yes, I would like to keep the screen lock function.