Is it certain that the airline knew this? From a quick scan here ok thought this was before he started.
We know that his paperwork was marked 'SIC' which apparently means that special medical supervision was required. This might mean that he had a chronic physical condition that needed to be monitored, but as it's been stated officially that no physiological problem was known to the airline, it sounds as if the medical monitoring was about his psychological state. Given that psychological problems manifested
while he was in Lufthansa training, and before he obtained his pilot's licence, I'd say LH knew there were issues with this pilot.