It's working again, not sure why though.
Stripped down the trigger mechanism to see if anything was broken or misplaced, couldn't find anything wrong but gave it a clean + re-grease.
Put it back together, semi now works fine. Nothing's changed in the way it's working, I don't understand at all.
Even weirder is that the cutoff lever still does not move, it can move if you do it manually, but nothing mechanically shifts it. Yet it still works.
Watched a video of someone elses gearbox cycling and the lever moved up and down as you'd expect.
HUGHHHHHH, MA BRAINS.