Me too. Sometimes I get the realm on the screen and I press (A), but then after about 2 minutes it kicks me back to the world screen and I says cannot connect to the realm. By the way it is my realm I own it.
I logged back in this morning after restarting and unplugging my xbox, but it still had no HUD. I saved and quit then went back into the game and my HUD suddenly appeared, so it is all fixed.
I was in the crafting bench and exited out then I might of pressed b and a and my HUD disappeared in front of my eyes. I think it was a coincidence that it disappeared when I pressed those two buttons because I then tried it again and tried other combinations. I also had a play around with the Opacity HUD slider and that didn't fix it, so I put it back to 100%. I also re- and de-enabled the huide HUD slider but that did nothing.
So you died instantly? Because the wither effect is supposed to last very long (about 1 min), and the heads are do quite a lot of damage when they explode on you. Overall, the wither is sooooooo OP on bedrock. On java you can make traps for it but it is so hard on Bedrock. Just saying.