Hello,

I am very sorry for delayed reply.

Thank you very much for the videos.
Now it is very clear.

This should not happen normally. So I recommend to disconnect everything that is possible first.
For example Wifi-Link and any power backup.

Does it mean that when the tail servo is plugged in in CH1, CH2 or CH3 port it is always initialized properly and is holding?
While when it is at CH4 it is not working sometimes, am I right?

Yes, that is correct.
But question is if the servo is always working well at CH3 or the problem is same on both ports?
So that sometimes it is not moving.