I tried to screenshot the bright flashing screen. That caused the bright flashing to take longer to go away (ca. 15 seconds instead of 2). On the screenshot, everything is normal.
Edit: I now think that this would occur when the lighting conditions are changing fastly. I still don’t have an idea to reproduce this. I have that not only in the bus now, but I haven’t noticed that in the nighttime.
I have had these bright flashed since last fairphone update. They seem indeed be occurring mostly when changing from light to dark environment (out other way around).
The flash is far brighter than the brightest setting of the display. Test is not readable anymore and colours are nearly white.
I’ve also started getting the flash described, I don’t remember it happening before the software update but now it happens for a second or two almost half the times I wake up the screen (not any other times though). I also still get the flickering low brightness problem but adaptive brightness has been disabled for some time.