I’ve seen this (or something similar) a couple of times. From what I can tell, the communication between the Raspberry Pi in the controller and the microcontroller that actually drives the stepper motors is getting corrupted.
The most common cause of this is EMI (electromagnetic interference). Brushed motors like the one on trim routers produce a lot of radio noise, due to the way they work. That noise can travel through the router’s power cord, which then acts like an antenna, making the problem worse.
This is also the reason that some people experience “blanking” on their screen. That same EMI interferes with the HDMI video signal between the Raspberry Pi and the screen.
To address both issues, I put the Makita router’s power cord in braided metal sleeving, which I grounded. Both the HDMI blanking and this occasional communications issue went away. Haven’t seen the problem in at least 6 months. This is the sleeving I used: https://smile.amazon.com/gp/product/B01BIBQ940
I recently switched from the Makita to a 2.2 kW Huanyang spindle and VFD about a month ago. Also haven’t seen either issue since then, as everything is well grounded to help deal with noise.
Here’s a picture of the sleeving installed on the router’s power cable. That crazy extra plug wire-nutted on is purely for the ground-line. The white and black are capped.
