The texture in question is whbigblocks01ssmask.dds, I left a comment on the mod page, but no reply or updates since. So assume they are busy, pretty trivial thing to fix. All you have to do is open the dds in paintdotnet and resize the image from 1025x1025 to 1024x1024. I saved and ran the texture through cathedral asset optimizer too. So it should work normally now and behave the same as vanilla textures.

It may be an overreaction to say that this incorrectly scaled texture may crash your game, I am still new to working with textures and most of what I know is from reading from forums and other mod pages. So disclaimer, I could be wrong to say it may crash your game, but it could cause problems. What problems? I do not know, but the rescaled texture is in fact correct and working. So if you use Ancient AF Windhelm - Windhelm Retextured, I strongly reccommend you download this file too.

It works for the 2k and 4k version of the mod, because this texture is the same for both packages.