So many variables here...
But at one venue at which I occasionally play, this was happening to me pretty frequently. After much frustration and trial-and-error, I found out it was some sort of interference with my WIRELESS. Phones, WiFi, who knows? But if I run wired there, I'm golden. If not... risky. Same exact symptom: notes stop, and then BOOM, all at once. Occasional "late" note or two as well. And that also gives me great cover when I blow a lick- "What? It's my WIRELESS, guys!" (*hiding Zendrum's midi cable behind leg...!)