Homing position offset after power cycle (happen randomly)

Hi All,

I would like to seek your expert advice and experience on Yaskawa Sigma7 motor with Mechatrolink 3 connection with MP3300 controller.
I am doing zero point return or homing based on c pulse plus an offset and if i do not power it off, the homing position is always the same.
But once i power on off the machine, sometime it will home correctly and sometime it will home not properly.
I have change the motor, the servo pack and even the encoder cable but still this homing position out of position will happen randomly.
I would like to know if anyone of you encounter this type of case and how to go about to solve it?
It is doing 90 degree rotation movement and from motor to my fixture is by a coupling. My mechancial engineer have check and feedback there is nothing wrong
with the mechanical portion of the fixture to the motor. I really need some advice and it is bugging me and i can't seem to fix this issue.
Thank you all in advance for the advices render!