Mine used to do that a lot. What I did was simply bend out the bottom of the metal strip on each sheet of film with my fingernails enough for it to grab. Also, when I pulled the film, I would feel to see if the pod was in or out of the holder as that's the only way to know if the holder grabbed on properly.
But if you bend it too much, it will stick and not process...
To take apart the holder, you just need a wide flat head screwdriver. The entire holder is held on each side by 2 U shaped clips (they have the slots for the Graflock holder in them). Once you manage to remove those, the whole thing is pretty simple to fix.
There might be a film end strip stuck in it... It's always hard to see.