Throttle RC Channer is not stable, jerks up and down when moving stick slowly

Hi guys,

I have a tinyhawk II RTF kit. Recently, I had issue with motors not arming, so I removed motor connectors and soldered motors right to the pads. Day and night difference.

But right after that I started having an interesting behavior:
When I fly, when moving throttle gradually up and down, the RC signal is quite jerky. Mostly observable in 2 points on the graph where it dips a lot before resuming back to normal level for split second. I suspected it might be motors and my soldering, but when running motor from BetaFlight, they are spinning stable.

So I measured the input from transmitter in Betaflight Transmitter tab and that’s where I saw it. All other Axis are fine, just the throttle one one is jerking up and down when I increase or decrease the throttle around specific area.

Any help please?