ADC read error when powering RC servo from 6v rail

Unable to repeatedly read from ADC while powering a RC servo motor from the 6v power rail.
Produces error "can't read iio adc fd: Resource temporarily unavailable" and crashes the program as well as the active terminal session. I'm able to reset the SSH connection and get back to a responsive command line, but am unable to re-run any librobotcontrol functions or programs until the BB is fully restarted.

I'm able to power and control the RC servo motor completely from the BB with no problem, as long as I'm not reading the ADC. I'm able to read the ADC with no problem, as long as I'm not powering the RC servo from the 6v rail. I am able to read the ADC, generate RC servo pulses, and have the 6v rail enabled, as long as I'm not actually powering the RC servo from it.

This leads me to believe maybe the RC servo is pulling too much current and pulling other system voltage rails down for a moment, causing ADC read errors. But the RC-servo motor only pulls 500mA, so the on-board 4A supply should be sufficient. The attached LiPo battery is fully charged as well.

I'm using a BeagleBone Black with Robotics Cape. Tried two separate Robotics Capes and saw the same result.

Kernel: 4.14.71-ti-r80
BeagleBoard.org Debian Image 2018-10-07
Debian: 9.9

Currently running on a:
MODEL_BB_BLACK_RC
Robot Control library Version:
1.0.4