Ok. That's not good since it means there could be varying levels of frequencies at what you're affected by which makes solving it totally unique - not good for those who can't afford time or money by buying suggested equipment that might work.
This might be a interesting test: Have a variably flickering screen, start at the max rate and lower in increments until you notice symptoms.
It's not going to be possible to solve this if we can't identify with numbers what affects and what doesn't.
Is there any level of frequency that won't cause headaches? Kinda goes back to this:
The reason I state "no flicker" instead of "no PWM" is that it technically does use PWM at 100Khz
Can it be adjusted to 120Khz, 150, 200?