My previous laptop (an HP EliteBook, the exact model escapes me at the moment) had an issue with Linux drivers where it would sometimes crash. When it crashed, the laptop's screen would quickly flash bright-dark-bright-dark... To my eye it looked like one garbage frame with mostly bright pixels and one frame with mostly dark pixels.
Nothing weird so far - just a driver bug right? The weird thing was that when I rebooted the laptop after such a crash, the screen brightness would still slightly, but visibly blink in the same pattern, while the monitor was showing normal boot screen and later the login and desktop. The flashing would get less and less noticeable and kind of ring out by itself after a few minutes. After that the monitor was just working as normal.
I can't think of a good reason why the monitor would keep blinking like that after a reboot. The best explanation I had was that perhaps some kind of adaptive algorithm for image postprocessing in the LCD driver had rolled off into an extreme and needed a while to get back to normal parameters. But it seems unlikely anything like that would have time constants in the range of minutes. The other possibility I thought about was that the blinking after a reboot was just a illusion created by my eyes, but I found that unlikely. I never saw anything similar.