"prearm: 3D fix need" but 3D fix is show

Hi Folks,
i have weird issue and i cannot solve it.
i build new platform witch is H Copter, i have FC Matek F765 witch arducopter 4.0.3 and GPS module Drotek zed f9p on board, on the ground i have second zed f9p to get RTK. like a telemetry and rc signal i use rfd900x.

I done few test fly and everything was ok, but sudenly after change battery to next flight i get error “prearm: 3D fix needed”, at the same time my GPS onboard shows about 20 satellite and 0.5-0.6 HDOP.
i am fighting with that issue few days. i change firmware in FC to older, bring all settings to default - in FC and in GPS module but there are still has the same issue.
anyone know what go wrong?


This message is missleading and we are trying to fixing it.
The GPS is fine, that the EKF that isn’t settle yet… check on your MP picture it is red

Hi khancyr
behind the “red” EKF is hiding: velocity_horiz off and pos_horiz_abs off
do you know what that’s it mean?

in quick research i see that corresponding to compass error but i don’t have a compass onboard.
to be honest i start with compass hmc5883l onboard but my platform generate big interference, compass/motor calib shows above 35% interference and i decite to disconnect compass. after desconnected compas i make 3 flew and everythind was fine