I have had that happen to me before, but only every once in a while, and that's if I haven't used the account for a long time. I think it has to do with Mbin's oauth refresh token expiring (I'll need to check for sure).

I'll admit, the feed pages need better error messages too (instead of the generic message we have now).

Not a solution, but anytime you need to re-login like that, you can skip the account removal step and just sign in as usual; it will automatically update the accounts credentials.