Tailsitter only 1 control surface move

I am building a dual (fix) motor tail-sitter running Arduplane v4.3.0.
My param as follows :–
SERVO1_FUNCTION = 4 (Aileron) SERVO2_FUNCTION = 19 (Elevator) SERVO3_FUNCTION = 73 (Throttle Left) SERVO4_FUNCTION = 74 (Throttle Right)

During bench testing in QSTABILIZE mode, and the motors are pointing upwards, only the right control surface responds to the elevator stick after arming and raising throttle stick. The left control surface does not move at all.
When moving the rudder stick, both control surfaces respond.

Please advise what param I should look at to make the left control surface respond. Param attached.
Thank you for any assistance.
Tailsitter.param (18.0 KB)