TM MP7 not locking back correctly

[Trouble]

My TM MP7 had started to develop an intermittent problem of not locking back on empty every so often. It was firing fine, just occasionally taking a few shots on empty to lock back.

I thought it may have been the colder weather so started using Ultra rather than 144, same problem.

If you hold the gun up and fire it, it locks back fine.

It happens inside, in the warm as well.

I thought propane may sort it, so today installed the Creation reenforced nozzle and started using propane. Wow, those creation nozzles are good! But still same problem, kicks like a mule but won't lock back 100% of the time, takes quite a few shots after empty (on semi or auto) to lock back.

Any ideas guys?

As a side note, I also ordered the FE aluminum nozzle head, which didn't fit well with the Creation Nozzle. Oddly. Worked fine with standard TM nozzle, and the creation nozzle works fine with standard TM nozzle head. Just not the Creation and FE together. Weird, anybody had any experience with the FE nozzle heads?