Quite some years ago now, I flew with (and trained - or tried to) a captain who was eventually (after three *** years!!!) "let go", who every other pilot (including the trainers!) in the airline, except to the chief pilot, (who was a friend and who'd employed him over the phone), was sure had a cooked logbook, if not licence.
He came in as a DEC, and if he really had been a captain before, God help us all. Everyone in the airline thought he'd been an FE at most in his previous airline. He eventually got chopped when he transferred to another fleet - (after three years of scaring his crews senseless on the previous fleet) - and really scared a training captain on the new type during line training.
As far as I know, he returned to his home country (that big one north of Mexico) and continued to fly.
In a similar vein, three DECs arrived at a very well known major South East Asian airline some years ago and aced in their sim training, but once out on the line, had major difficulties dealing with enroute weather and even moreso, all those little pre-departure problems that a captain has to deal with before engine start.
Turned out they'd been sim instructors on the type they came to their new airline as DECs - but actually flew the line for a couple of weeks before that became obvious and they were terminated.