Bad yaw control

Hello, today I tested my quad after a while and was really scarried with yaw control. Roll and pitch were really nice but the yaw almost uncontrolable with my RC stick. Its reaction to yaw stick from RC was too sluggish. As sluggish as I almost crashed the copter.
Here is the link
I wonder if it can be related somehow with compass errors.
Second thing, which can’t be seen from log is - one motor (nr. 2 - left rear) spins really slowly in contrast of other three motors. Dspite of this slow rotation of one motor the copter is leveled OK. It is like the propeller on motor 2 has much higher pitch than the others, therefore makes higher lift and slower rotation of motor is then required. But all is the same - motors, esc and propellers.

Can somebody hlep me with what’s wrong with yaw control?
Here are some facts:
FC is pxfmini on top of RBPi3
Arducopter of v 3.5.7
motors sunsysky x4110s
esc Tmotors air40A