Preflight fail: mag #2 selftest failed

Hi everyone,
I’m building a hexacopter with Pixhawk 3 PRO flight controller. I’m at a good point, but I’m experiencing strange behavior.
If I try to start the motors when the “flight controller” status is “Ready, no GPS” (blue blinking) everything is ok. In this case, the state passes, rightly to “Armed no GPS” (Blud solid). The problem arises when the status of the flight controller changes to “Ready, GPS lock” (Green blinking). From this moment the engines can no longer be started (armed). Why? The moment I try to arm the motors, I get an error (Red Blinking) with error “PREFLIGHT CHEK MAG2 FAILED”.
The calibration took place with Flight Controller connected to the “external” GPS-COMPASS.
Is this a bug? The onboard firmware is version 1.8.2.
I would be grateful if you could help me in this regard? Could it depend on the external GPS-COMPASS?

Thanks a lot