If you do a 3rd burst fail, then wiggle the mag and listen carefully can you hear the BBs move up?
Sometimes the mag isn’t aligned right and so BBs don’t flow too well, otherwise you may want to change your mag springs for stronger ones, or just get different mags.
You can check the bucking is not an issue, if you pop a single BB in it should sit in the lips of the bucking, and a very small nudge should make it fall through the lips, if it takes lots of effort that is not good.
The other potential is that at 24rps or whatever your firing at, the nozzle may not be staying ‘back’ long enough for a BB to get in front of it, this is normally resolved by a tappet delay chip.