With the newest 1.10 update and the new default texture pack it seem that some textures got corrupted or so. I am not sure what all textures are missing, but so far these are the known ones from me and a friend:Ghast, Slimes, Endermen, the side of Furnances/Droppers and anything else that share that texture, Sheep, Spiders. Bellow is just a two examples of it. 

How to replicate it:Play Minecraft bedrock  Switch on a realm that you are not hosting. The Realm must have been going for before the 1.10 update(not sure if one that been set up after  1.10