Update: Managed to test ride the bike properly only now, and the problem still persists.
From 3rd gear and up, when I let off the throttle on high-to-top rpms the bike shuts down. I can keep the rpms up no problem but every time there's a drop in the rpms the bike dies.
Can't hear any odd sounds from the engine, bike starts well, picks up rpms well, low to mid-high rpm range works normally and the problem is not present when the bike is in neutral, only when the engine is under load. Air screw did not seem to have any effect.