Just for shits and giggles, try some Bastards if you have them and see if you have any luck with them. I have the hardest time getting both Madbull .28 (haven't tried their other weights) and KSC / VA of any weight to feed in many of my mags. Seems that I have the same symptom as you. Generally (at least in the P90), semi or shorts bursts are ok. But in longer auto burts, they stop feeding, I remove the mag, and can see the next BB a bit down the feed path. I give the mag a tap, and it's good to go again.
The only BBs I've tried that will feed reliably every time in my AK and P90 mags are Bastards.
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