That fixed it for me, too! Thanks!

At some point a couple days ago, I stopped being able to update icons or banners on communities. I’ve tried everything I can think of on my side, including appointing a friend as a mod, who was also unable to edit the images.

[EDIT] I had both English and Undetermined selected somehow, and as per user suggestion I fixed that, and it worked! I can now update images, I just had to select ONLY undetermined.