anti-flicker

I have been having a very hard time removing a flicker from my 4k videos. It is especially noticeable on vertical white features, like a railings or trees. It often occurs on a roof, with the roofing tiles causing a resonating wave as the drone pans across. I've tried to shoot all manual...

I was looking thru my settings yesterday after the update and I noticed that I cant change the anti-flicker settings from 50hz (all are greyed out). I have it in NTSC, 4K, 30 FPS?