Airspeed Settings

I am Flying the HERO 2 VTOL with v1.14.3 and I have issues when preparing Landing. I Have airspeed trim to 17 m/s using 44% Throttle. When sinking 1.5m/s it first is reducing throttle, to maintian the airspeed, then suddenly the airspeed gets faster and instead of decreasing throttle it increases throttle.
I have that behaviour now on different FCUs mainly I use Holybro 6X. Issue is i get to high speed and the VTOL goes crazy. But otherwise I have no issues. Only when I suddenly gett this high speed. Can someone pls help

Flight log will be more helpful in understanding the problem which you are facing.

I have here a short screen record on what happens.
vtol-airspeed
Here you can see what happens. I have set the Airspeed Trim to 17m/s when the UAV starts to lower altitude, I keeps the 17m/s for some seconds. Therefore the FCU decreases Throttle. Due to change of UAV heading the wind comes from other direction, he needs to increase throttle again to maintain 17m/s but after a few seconds the airspeed goes 18m/s - 19m/s 20m/s 21m/s and instead of lowering throttle is increases throttles, so the airspeed got even higher.

Hello, Have you tried manual flight?
When it turn flight, the pitch down is visible …
I think it’s raising the throttle to keep it level.

When I fly manually everything is fine, I have this behaviour when flying Mission Mode, Airspeed schould be 17 but when it gets higher it also start to turn more had because of the higher speed it gets