A330 & A380 bifolds also jam easily if the waste container falls out. Had to unclip one just yesterday after landing. Newbie crew looked at me and said "I didn't know you could do that". I think it's something you just learn while flying rather than something that is "officially" taught in training. Getting people out of the plane in an evac kinda overshadows opening the lavs.
It's even worse if the object is slightly left of centre because then the door jams a lot more than if it's just sitting in the middle- in the middle you can just give the door a good push and usually the object will move. Obviously in the case of a person it'd be a total removal. Ok so not all the crew might know how to do it but I doubt there'd be many cabin seniors flying who wouldn't know how to open them if needed. It's pretty obvious how to do it & if you didn't learn in the first month or two online I'd be pretty surprised.