Qplane(v3.5) ,mode Qhover to Qloiter translation not stable

At first I fly my quadplane in FBWA mode,and then I slow down my plane and then change to Qhover mode, it acts well . I control the plane in Qhover mode until the plane stabe,without horizontal speed.At this moment I change to Qloiter mode,beyond my expecting,plane didn’t change to Qloiter stablly,the plane raise its head heavily,making strong noise and then loiter well.

I want to know why the translation is’t stable? Can the plane head don’t raise?