Read the previous posts ... if your heli is CCPM then ALL THREE OF your servos perform the Pitch FUNCTION ... not just the one plugged into the Pitch CHANNEL.
Don't confuse the Pitch CHANNEL/SERVO with the Pitch FUNCTION (what makes the blade pitch change).

For a 120° swash config (eCCPM) ... ALL THREE swash servo/channels (Pitch, Aileron, & Elevator) perform the Pitch Function and ALL THREE swash servo/channels perform the Elevator function.
This is why you need all your servos to perform the same.

If you had a non-CCPM heli (ala TT Raptor), then the Pitch channel/servo can be different because only the Pitch channel/servo performs the Pitch Function.