This Is A Very Popular Bug And So Easy To Do I Have No Idea How You Have Not Noticed This Yet.

The Way It Works: If Im Riding On My Horse And I Dismount Him Manually Sometimes He Just Vanishes And I Have To Re-join To See Him.

From What I Know It Doesn't Happen When It Automatically Dismounts You .

And It Also Happens On Multiplayer Servers.

To Recreate: Ride On Your Horse And Dismount Alot Then The Horse Should Vanish.

And About The Popularity Of This Bug Out Of All People It Happend To PewDiePie Multiple Times.

So Please Fix This Is A Sort Of Serious Bug.