Copter loosing height from one wp to next wp during auto mission

my copter (zmr250, 3S lipo, Emax1806, pixhawk lite, copter 3.3.3) ist loosing height when going from one wp to next during auto mission. Flying in ALT hold mode is working properly.
Do you have an idea which parameters do not fit or what issue will help?
link to bin log:

kind regards, Gernot

Is it the right height when it reaches the waypoint?

when the copter reaches the waypoint the height is ok. the copter looses height on its way between the waypoints - but also regains the desired between the waypoints. Seems to be somehow not stable.