Test battery voltage, be sure that the RC has a strong battery, test voltage while travelling and while lifting. More than a 20% volts drop while running a motor is a red flag, Weak battery.

I would make sure that all the Power Cable that attach to the Access controllers are definitely tight, no loose bolts.

Next, take a good look at the SB 350 of the RC and the battery, be sure that the Power Tips are seated properly within the SB 350's.

Test the Keyswitch for voltage drops and for resistance; lots of techs ignore the age of Keyswitches and Ignition Switches.

Go to the Distribution Board and remove and blow out the K1 Relay. It might be very dirty or the coil might be very weak or have an open winding.

If the RC has more than 3,000 Hours, I would just replace the K1 anyway, that is a lot of hours.