Once again, just a rough guess again as I'm not familiar with your exact model..
Now we've ruled out a foreign object in the slot, next step would be to check the condenser you are trying to slide in. Take a close look all round it to see if all the plastic moulded parts are all full clipped together and there are no gaps or obvious sign of damage.
This may not apply to your condenser, but I've seen issues with washing machine detergent drawers that have a little plastic spur that clips into a latch inside the machine. The purpose of this is to simply hold the drawer closed when the machine wobbles on spin cycle. Does your condenser have a latch or spur at the bach that locates into a catch inside? If so, this could be slightly bent out of shape and a gentle adustment could get it to line up with the catch again and allow it to be pushed that extra 5mm as it latches in place.
Just a guess without seeing exact parts, but fingers crossed!
Rupert
November 2019