The hitbox on skeletons is bugged.
If skeletons are in a 1x space (as in a monster farm) you can only kill one skeleton at a time.
You can hit one skeleton, then you have to wait until the falling-and-dying animation finishes before you can hit another skeleton. You should be able to hit skeletons continuously.
Example: swinging with the sword repeatedly will only hit one skeleton and will not hit again until his death animation is complete.
Thank you!
Linked issues
duplicates 1
Comments 2
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-9999.
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Confirmed. This behavior is seen for any kind of mob, not just skeletons. I believe they all retain their hit boxes for as long as they exist in the world, including while going through their death animations. You cannot strike a mob that is in the shadow of another mob's hit box.