The keyboard brightness automatically resets to full brightness after some random amount of time (10 minutes, an hour etc).
Sometimes the color also resets to purple/pink and after such a reset the “keyboard status” (oled menu) reports a “syntax error” but comes back as normal after a “keyboard reset” using the oled menu.
In my case this was caused by reform-power-daemon. It has fixed brightness values for plugged-in or unplugged.
Examining the logs showed it frequently flapping between battery and plugged-in states regardless of whether a power supply was actually connected.
Initially I commented out the lines in the reform-power-daemon that set LED brightness. However, after reading the rest of the script and seeing that it also changes the CPU power profile on state change I’ve just disabled the service for now.