On my realm with my friends we spawned the wither in the end. We killed it and then later decided to go back to the end. When we got there it was hovering over the spawn like we never killed it. I've tried everything, even turning it to peaceful but that only works for a short time. It seems that it may have occurred because we left the end and came back to kill it the first time, but I'm not sure.
Thank you for your report!
We're actually already tracking this issue at MCPE-62332, so I will resolve and link this ticket as a duplicate.
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