Usually it is because you are mowing way too low and the deck gets lifted above the hook so falls off.
They do need a shove to the right ( I think ) regularly because the torque reaction causes the deck to slide to one side of the lift rod and when it gets to the bend it will also fall off.
I think that was fixed in latter models.
have a good look at the fixed support rod.
Despite being 3/4" thick it it dose seem to manage to spring out of the bearing block in which case the deck will need to come off then both bearing blocks come out, get put back kn the shaft then done back up.
Very little space to work in.
I have a lot of widows in my run that insist on mowing the grass 1" and I will get called to refit their deck 3 to 6 times every season.