[rotorwrench]

That may not be a blocker ring problem. It's more likely a wear problem but blockers can get problematic. Thrust slack is taken up by snug fitting parts with the counter shaft and the main shaft as a whole. If things wear too much, the thrust load can push it out of gear. Even a worn 2nd gear bushing could be at fault. They like to do that when the load reverses and thrust changes such as letting off the throttle & engine braking in 2nd.