Rotax losing power during last 1000rpm

Hey everyone! Recently moved from rental kart leagues and endurace arrive and drive to owner-kart sprint racing by purchasing a used OTK 401s and rotax max. The engine supposidly has about 3 hours on it. After a bit of jet tuning, we got the kart running fairly well. However, I’m seeing a strange issue that crops up after running for about 10 minutes. At the end of the straight, the engine seems to fall on itself and not continue revving the last 500 to 1000 rpms to hit the limiter. At first this happens only evey 1 in 10 laps or so. But then it starts happening every other lap, eventually happening every lap itself. Here’s a screenshot of two sessions (first session where at the start of the day, where the issue barely happed at all, and second issue 1 hour later in the day - air temperature roughly the same - where the issue started happening every lap).

Apologies for the shitty screenshot, had to take it from another computer as I couldn’t get the analyses software to work correctly on this one