Airsoft Canada - Thompson Trigger

My Tm Thompson is almost 2 years old now. Around a year ago I put Systema 120 spring in it and various parts, including a metal bushings, anti-reversal latch, Systema torque up gears, piston and piston head. It has been shooting fine, but the other day before a game I noticed that when in semi the trigger would stick in the back position. I would have to flick it forward to get the gun to cycle again. When tapping the trigger for fast shooting this didn't normally happen. However when squeezing the trigger for acuracy, the trigger would stick. I was wondering if anyone knew what this could possibly be. Thanks in advance for any help.