I am guessing this is the Newer T05 that does not have the black sleeve that the assembly slides into that covers the top of the trigger. The older T05 had this cover that held the top cross bar and the long spring in place. On the T05 make sure when you install the pins thru the receiver that the safety notch is not in line with the pin. If not it will bind and can break the safety fork bar.I can tell you this much, the two aperture plates in there that hold the piston latch rod DO have to be facing the correct way. I had a similar problem early on in the setting up of my 12ftlbs destroked piston build on the RWS54 I have. Honestly at the risk of putting pie on my own face I can tell you that I THOUGHT the problem was the profile of my custom machined piston latch rod notch. After a LOT of back and forth doing testing and tearing it down etc I put the original piston back in and had the same problem. Then I realized it was the orientation of those aperture plates that was causing the locked action problem. Once I got them switched the rifle fired properly again. The trigger is a very robust design albeit with not the best feel or adjustment as some other higher end spring piston triggers but it is rather good. I went ahead and put the original plastic trigger blade in the mill and did the two screw modifications to it which helped a LOT. I am working on some other options to make it even better now. Once I get the Target stock completed I am working on I will get down to the trigger. Good luck with yours my friend..
DoNe plenty of T05's and the 2 screw mods. Never had a problem with them. The coverlets T05 I had the same issue. Cocked and locked but would not fire. PITA when the spring is compressed and the piston locked. It is correct that you can adjust the screws where the trigger will not latch and or not fire.
2 screw mods need to be respected. Also once set to your liking blue LT. On a brake barrel the I'll adj trigger is a barrel bender even worse on a lever gun for fingers if the bear trap fails. Also with the 2 screw mid spring work can improve the mod and trigger pull weight. Jmo