Read the statement by Michael Teeuw here.
Screen flicker when rotating screen
I recently completed my first MagicMirror project =D. Everything is working quite well, but… the only issue that I’m facing at the moment is when I set “display_rotate=1” in my “/boot/config.txt” (and then reboot) my LCD (TV) display is flickering. When I am changing it back to “display_rotate=0” my screen isn’t flickering. FYI - I tried the same configuration on a computer display and everything is working nicely.
Does anyone has an idea what to change in my current configuration when connected to the LCD TV display?
Thank you all, hope to hear from you.