Matek F405 std shuts down one motor on failsafe/RTH

[rotorrad]

Hi folks.
I'm new to small boards like omnibus, Matek, etc. I wanted to build a small fun quadcopter for the first time. I normally use Naza or eagle tree for 450+ quads. I took my time, started with omnibus F4 V4 had a problem with every radio that I own, probably a bad clone. Got the quad built with several revisions, not much space for what I'm used to.
Anyways finished built with Matek 405 STD, Matek VTXPDB hub, and Matek Ublox mn8. All in blue on 13 sats outdoors able to arm, etc. Radiomaster tx set up with three pos flight modes + arming switch. Modes are: Angle, Pos Hold, Failsafe/RTH.
When I was testing it outside (luckily without props) after switching to failsafe, motor 3 shuts completely.
What have I done wrong?