I started a new world in a Realm this 3 days ago.   I have found that at times some chunks do not render their textures.   This happens in areas that have been previously generated and loaded.   Logging out and back in doesn't not seem to correct it.   I can download the map locally, open it and the textures will properly render.   I can then upload that map back to the Realm and the glitch is fixed.   This has happened 3 times now in the past 2 days.   

Here's a YouTube video:   https://youtu.be/ORzrxuoPg10