I recently had to notice that the screen of the FP3+ sometimes slightly flickers in the lowest brightness setting. It’s very subtle, so I would call it rather a fluctuation.
After experimenting a little, I found out that this is not random but likely caused by fluctuation of the voltage caused by CPU load or the speaker. Typical situations are e.g. the screen going a little darker e.g. while scrolling or seeking in an audio file and a slight flicker when playing music on the speaker or having a handsfree call. (During the latter I first discovered the issue.)
It seems that this effect is decreased but still present when the phone is connected to USB power.
Am I just very sensitive to brightness changes or did someone else also notice this effect?
Very interesting, will keep my eyes open for it 
but strange it doesn’t happen more when the battery is under a heavier load as in very bright and the CPU/GPU processing a film/movie/video