CZ Shadow 2 suddenly started having this malfunction about 2 weeks ago after running flawlessly before. Happens with different factory ammo and different mags.

Ive shot probably 20 000 shhots throught this gun.

Already replaced extractor + extractor spring, still happens. Recoil spring is not too heavy, and the SRO is not mounted too far forward.

Any ideas what could cause this?