I would say it is not draining properly.
It may be draining enough so as not to bring up an ‘F3’ code but not completely enough to register empty at end of cycle.
OK – so the drain sump is clear, I’ve drained the machine using the front tube, run another drain cycle as well and the door still wont open automatically.
Is this the time to call someone in to look at it?
Have you checked the instruction book as it sounds as if you have the child lock activated, hence the door won’t open automatically at the end of the cycle?