Simply put: While in fullscreen, on the Windows 10 Edition (not java), if you alt tab out while in a realm you are kicked. Minecraft build if you need it: 4209675
How to replicate:
Go onto a realm.
Make sure you're in fullscreen.
Alt tab out and alt tab back in, even within 5 or so seconds.
Wait for about 10-15 seconds, as it looks as if you are still in the realm, but network connection is lost or something of that sort.
Related issues
duplicates
Comments

We're tracking this issue as MCPE-19393, so this ticket is being resolved and linked as a duplicate.
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