Tailsitter Return mode do not work?

#1

VTOL Duo Tailsitter
version V1.9.0
I test it in multirotor mode.
I set return alt 5m, it work all right, this show mag sensor is OK.
but I set return alt to 20m, when activate Return Mode, it rise to about 20m,
and then fly away.
Can any body help me?