I am not seeing ANY X on Findagrave.
FindAGrave often has slowness issues, where no photos are displayed, but I have NEVER seen an X instead of a photo there.
Yesterday, on my own home page on FindAGrave, my profile photo was not showing. Instead the name of the photo was displayed. I see that regularly, especially on weekends and holidays. Again, I have NEVER seen an X on FindAGrave.
OP wrote "The last few days I have seen black "Xs" for my photos at my AMT." Not the same thing, as I understand it.