Exactly how is it stuck?

Mine does this alot

I find a few tough pulls or waiting a while for it to snap back...
I've had this issue for 2 years or about. not yet found or checked for a solution, Is your issue intermittent like mine or all the time?

If all the time it might need new "firing-Pins" or what ever it uses

mine did this and then when i took the belt out to see what was wrong it rolled up and wouldn't come back out..... so in the end i just got one of the internet and fitted it now works perfect

seat belts work by gravity.. so if the belt is at an angle it shouldnt be in it wont work... i would make sure its all bolted up ok