The shield bar disappears when you travel to and from the nether.

Put the summary of the bug you're having here

What I expected to happen was...:
Describe what you thought should happen here
When I travel to the nether, my shield bar does not disappear
What actually happened was...:
Describe what happened here
When I travelled to the nether, my shield bar disappeared.
Steps to Reproduce:
1. Put on armour
2. build a Nether Portal
3. Travel to the nether
4. The shield bar should disappear.
5. If it doesn't, if you travel back to the overworld, the shield bar disappears.