the wither health bar disappear and refuse to die

After the aquatic update in Minecraft, I started a new world to get the most of the new things in the ocean. I tried to finish the game and kill the wither in my way. I could not kill the wither because after he killed me for the first time, his health bar disappeared. it did not matter how much I hit him. Every time I start the game again, his health bar will show up but it will disappear again after I die for the first time. I tried so many things but it did not work.

 

I forgot the whole thing till I bought a new xbox one x. I downloaded the game and tried to kill the wither but the same thing happened again. the health bar is not visible and he is not dying. I risked my world by turning it to creative to kill it but it still did not die. It did not matter how much I hit him and the health bar was not there.

 

so is it a part of the game now that if the wither kill you once you cannot kill him or what?