This bug has also been added as a comment to MCPE-47294      

Several days after the above mentioned Bug report was created by SilentWhisperer, our Realm started experiencing something similar. I won't call it exact because we are in a vanilla Minecraft Realm and our players are not logging out on glass or knowingly logging out over lava.

The first occurrence of this bug happened when a player was randomly disconnected from the Realm while mining. Upon logging back in, the player spawned under the world. The death message was "player fell out of the world."  Three days later the same bug occurred to this player again, also while mining. During the second instance, the player was with a second player when he was randomly disconnected from the Realm. Upon rejoining, the second player could see the avatar of the first player render on the block he was standing on when he was kicked, however when he fully entered the Realm, the second player watched the first players GT randomly descend through the world. The death message was similar to the first one. 

Within a few days this bug occurred to another player. In that instance the player was joining the Realm for the first time and "fell out of the world" three times in a row. I watched as his avatar appeared on the spawn block and then immediately, upon full rendering, I watched his GT rapidly descend through the world. 

Similarly, several players, including myself, have been randomly kicked from the Realm since the 1.12.0 release. Upon rejoining the world, we've found ourselves under (and sometimes adjacent) to the location we were standing when we were kicked, and several blocks under ground with our bodies actually IN the blocks and taking damage. Occasionally we've been able to rapidly quit the game and re-log whereby the game has put us either on the original block we should have been placed on in the first place, or on a safe block somewhere in the vicinity. 

We've attempted to compensate for this issue by logging out without our gear, etc. and by taking screen shots of our location so that another player can come and dig us out if needed. 

(Please see attached screen shot where this happened to me a few days ago)