Must admit as soon as TCAS fails I tend to start looking round the cockpit for something else that has failed. First suspect is the Rad alt.
Its not officially broken until you land at the other end after you have pushed.
And with TCAS I wouldn't be surprised after you landed and you did a black aircraft reboot it didn't self heal.
It depends on the aircraft type your flying. If its a retro fit TCAS installation or if its a installed as new and fully integrated into the aircraft data buses. Its not common its "just" the TCAS processor that's failed it usually something else that links into it. 80% of my issues with TCAS failures have been something to do with the rad alt. And failing one of them properly with a CB pull (on being told to by the B2) has unconfused its little brain and its started to work again.