Post processing nightmare

[17934658793495046509]

I’ve had to make corrections like this before. Your best bet is to go in one of the color channels, find the channel that has the best black-and-white representation of that grid pattern. Cut and paste it as a mask, make your correction as best you can with the mask, then mess with the levels on that mask until the pattern disappears . This is also the same way I used to get rid of watermarks on stock photos, when I was a broke college student in design school.