So i own a Realm and i have several Shulkerboxes to kepp my Stuff organized. One day after building i place them all down and log off only to return and notice that 2 Shulkers have been deleted comepletly. Like they are gone.About a week later i check on my shulkerbox room where i keep them all and there are 6 out of 8 missing. 
By checking with Onix i discovered that my Room is split between 2 Chunks but there were Shulkerboxes deleted in 2 adjacent chunks without reason. Can't really show proof cause they are gone but it has happened twice in 8 Days. And it affects a big Part of the game.
It's a Realms exculsive Problem never had it in Singleplayer.
Also nobody could have stolen them cause the times of the last backup of the realm machted up with my Logoff dates with no further players playing on both occasions.

EDIT:
Made some screenshots. The date of the realm copy is in the world name on the pause menu screen. Also Onix Chunkborders are enabled that are the yellow lines.