It might be a problem with the piston not coming back far enough. I just saw this issue in a rifle in the shop, what is your piston/cylinder/cylinder head combo?
This is not possible because the bolt pin/piston lock holds the base of the spring guide in place. Removing the screw entirely and removing the rod might do something to affect the catching of the piston, but even that is unlikely. If it's too tight you might not be able to raise and drop the bolt handle with ease, but the bolt itself should still move.This is kind of a long shot, but how loose is the screw on the back of the bolt? I know that if it's too tight, you can't move the bolt. So maybe if its too loose it won't catch.
I had a similar problem where it got stuck either immediately after pulling the bolt back or halfway when cycling it forward, although it might have been the way I was pulling the bolt back at the time(righty gun, lefty user). To fix this problem I added some lubricant inside the chamber and on the cylinder and it worked beautifully afterwards.I know from my utg that if I don't pull it "correctly" it doesn't catch... It will be stuck back but I can't push it forward until I nudge it back further.. super annoying..
I opened up the trigger box and everything seemed okay.
Huh?I also never took the trigger box apart.