Driver's side seatbelt locked

[bteoh]

The driver's side seatbelt got locked and would not extend on my 156 GTA. Tried pushing or pulling umpteenth times but it wouldn't extend.
I went out and bought a second hand unit from a slightly newer 2004 156. Worked ok when I tested it there but after removing it and taking it home, that unit also locked up and would not release. Anyone come across this problem at all? It seems to have a canister like device attached to the side of the seatbelt. I presume that gets activated in the event of an accident. Car had not been in any such events and no error codes showing either.
I am stumped 😳

[bteoh]

Update :-
Managed to get the spare unit to work. Turned out that it had to be upright when extending.
However, not sure why the original failed in the first place.
Someone knowledgeable here might know?

[bazzbazz]

Just age & wear & tear of the locking mechanism, it happens.