Edited: Description changed to match a Proper Bug Report.
No Addons Used

HUD completely disappears when changing difficultly in the options menu while in-game

Notes:

• Bug may appear at random intervals while playing.
• Unknown if Bug happens on Offline Worlds.

Steps:
1. Enter Options Menu while playing on Realms
2. Scroll to 'Game' tab, change difficultly from 'Peaceful' to 'Easy/Normal/Hard'

Observed Results:
HUD has disappeared (Armor, Health, Hotbar and Hunger Bars (See Image))
Entered Options/Video, all option are switched on (See Image)

Expected Results:
HUD should remain on-screen when difficulty has changed.

Attached 2 Screenshots.