5V/serial weirdness when using FOC

I'm using a 4.12 VESC in FOC mode to run a 16" hub motor. This works without any problems, but I wanted to display some data on a screen.
For this, I am using a cheap Arduino clone, which is connected to the VESC 5V output and serial. (library in use: https://github.com/SolidGeek/VescUart​)
In BLDC mode, everything works the way it should, but when running FOC, the Arduino "freezes" at random times. It only starts updating the screen again upon restarting it.

The only thing that I could think of that would cause something like this is a temporary drop in voltage on the 5V output when the VESC is under load, but I've measured it and that doesn't seem to be the case.

I'm completely out of ideas, so any help would be greatly appreciated!