Nuki motor blocked - impossible to use the backup key to open


Last week I had a serious issue with my nuki lock 3.0. It seems that at some point it got unsticked from the door (only way to use the lock with my door), resulting in a “motor blocked” error message.
The important point is that it was impossible to open from the outside, although I have a cylinder equipped with an emergency function (meaning you can open the door even if there is already a key turned on the other side). The only case when you can not open the door with an emergency cylinder is if someone (or something) actually blocks the key on the other side (= does not allow it to turn freely).
At the end I managed to get the nuki lock to work again and got inside with my key.
But this frightened me. Like a lot.
How is it possible that the device actually locks the key, meaning does not allow it to turn even if physical force is exerced from the other side ? This looks to me like a major flaw and a significant risk to be unable to open the door in case of malfunction. It could even be a safety risk in case of emergency (not being able to leave the place in case of fire for example).