Skid Steering using Brushed Motors with Relay Issue

Hi, I am using ArduRover 3.5.2 on pixhawk 4 . There is a weird behavior when I used AUX 5 and AUX 6 for RELAY_PIN and RELAY_PIN2 and it only happens when reboot. The rover turn left when I push the throttle stick to right and turn right when I push the throttle stick to the left. It only happens once and everything will be back to normal until I rebooted the Pixhawk.

It only happens for AUX 5 and 6. I got no problem using AUX1 and AUX 2. But due to my application, I need to reserve AUX1 to AUX4 for servo applications.

Anyone managed to solve this problem?