I was playing in version 18w15a when I noticed that the nether fortress(loaded in 18w14b) I was exploring had Nether brick fences with the wrong connecting texture/model. I went ahead and launched another world(in 18w15a) to see if I could find any more Nether brick fences with the same issue, and was also able to find them in the newly created world. I was able to fix the block textures by placing blocks around the affected Nether brick fences.