2 ender dragons at once?

So i was in the end fighting the ender dragon for my first time in the world and out if no where 2 boss bars appear. and i was confused, i thought it was a display error. nope! there were 2 bosses at the same time. I am going to make other reports cuz i was told to separate each bug. But the ender dragon still had the one shot kill breath, even with full diamond! i got some video footage that i will link so you can see it. this occurred in "cubed creations: 1 block challenge". https://youtu.be/mjqvx98SKIw