There is a bug when joining the Nether. Looking above the heartbar it is noticeable that the armorbar is missing. I noticed that, when I got attacked by punching a zombie pigman.

I became damage as if I would have no armor put on me. But on this linked screenshot on the webside Lightshot it shows that there is no armorbar even if I put on my armor in the Nether:

https://prnt.sc/mg89da