Hello there, I am having this problem for some time now, my brightness is changing automatically in two scenarios:
1. Same driver version, randomly changing upon startup when windows login appears, sometimes dark sometimes bright.
2. Different driver versions, with one is bright the whole time, with another driver is dark the whole time.
In first case with some driver versions starts bright but after entering a game for exam ple goes dark.
In the second case remains at the same brightness everywhere windows, apps, programs, games etc.
I have looked for solutions online but everything was about windows settings wich did nothing for me. I am looking forward for an answer, thank you.
Windows 10 x64, AMD RX470.
Check the manual that came with your monitor. Some of them automatically control the screen brightness. Mine does. But I have it disabled.
Looks like your not the only one having that problem with the BenQ. Try turning DynamicContrast on the monitor to 0.
I was just looking at the manual for your monitor. DynamicContrast is there under Picture Advanced Menu. If it's greyed out, reset your monitor to factory default and restart it. Then look again.
It is greyed out indeed, I thought it is like this because is not available for my model, but if I change the picture mode I can change it, so nothing here because even when it was grey out was off, on 0. So my monitor it is not at fault, but thanks for your suggestion.
Darn! I was hoping that was the problem. I still think it's your monitor but I'm at a loss to say what could be causing it. Good luck.