The single claw extractor is inferior to a flat extractor which grabs more of the rim. With soft brass or Al, the claw can literally chew through the rim leaving the cartridge in the chamber, or worse yet, lying on top of the next round. Couple that with a slick slide lube which lets the slide move quickly to the rear, while the pressure on the chamber walls is still elevated, and you have a receipe for problems.
The 1911 fix works because the pressure into the cartridge base is such that the claw doesn't slip down and nibble off the rim. It's pushed firmly into the relief. This still lets a really slick lube job cause problems, but not all the time. With more viscosity my FTE's ended, period.
So my thoughts are these, see if the new extractor can be modified to grip more of the rim, put the 1911 slide/safety spring in the extractor plunger spring, and get more viscosity on the slide rails.
Just in case I'm wrong, would someone post the spring weight of the new plunger spring vs. the old plunger spring? If the new one is heavier, it might be that under certain circumstances it's too heavy, that is, it's pressing the case against the chamber wall too hard.
Blowback actions are way more complicated than they appear. Timing is a tricky function when only the mass of an object is controlling when something happens, and the other pieces have parameters which don't depend on the mass of the cycling element.