[MC-29463] Can't obtain achievement "Beginning?"

Try spawn a wither after you have done all the parent achievements.
E.G. THE END

and spawn the wither as said in the description of the achievement

all worlds tried: Overworld, Nether, End

and doesn't give it...

is this only happening to me or is it not implemented yet...

Or is it just a bug?

Linked issues

Are you saying that you can't spawn the wither or that it won't give you the achievement?

It doesn't give the achievement.

Picture of the wither health bar at the top and the achievement not given.

Duplicated in a Multiplayer environment. Still does not give "The Beginning?" achievement.