Impulse

could try changing the valves, may be sticking open a touch too long?

had a similar poroblem with my m92, could barely get half a mag out off a full fill. changed out the valves and it was ok

Thing is, before the cycling issue it was firing at least a full mag on a fill of gas. Half a mag in the winter, because it's such a small mag. I removed everything from when I had the cycling issue and even tried shoving in all the stock parts and it still had the same issue.

I've worked on a lot of pistols, because I tend to tweak mine to perfection since I use them so much more than most because boltie and MED, but this one has me at a loss for words. It has exactly the same build now as my p226 that works so flawlessly

I had a WE 1911 many years ago that had an issue like this. It seemed to cycle fine most of the time, but efficiency was piss poor & recoil was very inconsistent. I tried a bunch of things to make it work before eventually realising that the trigger disconnector was digging into the slide (and the harder the trigger was held the harder it was pressed against the slide, to the point that you could stop it cycling by holding the trigger hard enough)... in that case the fix was to simply add a shallow groove for it into the blowback housing so the slide wouldn't try to push it down more than was necessary.