You will probably notice the same issue with some roadside LED signs, i get the same on some signs and for some reason it don't matter if i choose 50 Hz we Danes use or 60 Hz.
You will also see it on some cars rear LED light, in video footage they will appear to flash or something like that, but you don't see that with your eyes.
I think it also have to do with exposure timing like weedeater say, in the daytime the camera might use 30 X 1:10,000 second to capture a second footage, but at night the camera lower exposure timing to capture more light for each frame so it will use something like 30 X 1:30 second to capture 1 second of footage at 30 FPS, and so at night the shutter are open much more than in the daytime where exposures are so fast that most time of a second the camera wait to take the next frame as each are made in 1 : 10,000 of a second V s 1:30 second at night.
Yoou can say it is a matter of the 2 things beeing out of sync due to exposure timings which are fast in the day but slow in the night, and that coupled with the fixed Hz rate of your phone / HUD screen cause the problem.
If you could lock your camera to the night time exposure timings you would not have the the daytime flicker in the HUD, but then your footage will be far too bright as the exposure timing will be far too slow for daytime.
you can try to put a phone with a speed app in the windscreen too, and you will probably see that behave different as the phone screen probably have another refresh rate than the HUD have.
