Backlight randomly turns off completely when changing brightness

Expected Behavior

Backlight should never turn off completely when changing the brightness.

Current Behavior

When changing brightness, there is a risk of the screen going completely dark and the device becoming unusable until a reboot. The device itself still responds to touch and is still usable via scrcpy.

This is exacerbated by enabling Settings -> On screen GUI… -> Force maximum brightness in OpenCamera, but can happen under normal use without it.

While in this state, if one shines a torch to the screen at an angle, the contents of the screen can be seen. This indicates that it is just the backlight that has completely turned off. I have been unable to wake up the backlight again through the sysfs controls.

This is a regression in LineageOS 23.

Might be unrelated, but the brightness curve doesn't seem fully consistent near maximum. There is a very observable "step".

Steps to Reproduce

• Either play with the brightness bar a lot, swiping all the way from minimum to maximum brightness and vice versa until the screen goes completely black
• Or adb root, adb shell, then with the screen on and caffeine enabled, run the following and wait:

while true; do for i in $(seq 0 $(cat /sys/class/backlight/backlight/max_brightness)); do echo $i > /sys/class/backlight/backlight/brightness; done; done

Device information

/codename pioneer /version lineage-23.0 /date 2025-12-04 /kernel Linux localhost 4.19.325-cip124-st8-perf-gbb4e518d8837 #1 SMP PREEMPT Thu Dec 4 07:25:37 UTC 2025 aarch64 Toybox /baseband 20200722_BY12O_Daily /mods microG

I have read the directions.