The Test giving Success is highly likely because Windows is silently re-using the existing cached connection (which of course, after the reboot, doesn't exist). Note that you can't connect to the same \\server from the same client using two sets of credentials at once (and Windows usually doesn't even try - it just re-uses 'current', which may not have the privileges for what the 2nd process is trying to do).
Did you try the various formats of user-name? You didn't say.
Did you try toggling which credentials first (Network > Advanced)?
Did you try the various formats of user-name? You didn't say.
Did you try toggling which credentials first (Network > Advanced)?