The bug
Some mobs strafe on certain blocks they move extremely fast (1.5 times as fast as hostile endermen), and move straight toward you instead of strafing. Just hit a skeleton in third person in Survival to reproduce, or let it walk on certain blocks like rails, they will go berserk!
Also noticed that if you run down a hill with a horse, the skeleton will "hover" or "slide" towards you.
Affected mobs
Skeleton
Illusioner
Piglin with crossbow
Affected blocks
air
chests
daylight sensors
enchanting tables
end portal frames
grass paths
farmland
lava
water
magma blocks
honey blocks
rails
slabs
soul sand
Linked issues
is duplicated by 16
relates to 5
Attachments
Comments 23
Could you make a list of affected blocks?
Confirmed for farmland.
i can confirm this with grass paths, chests, slabs, magma blocks, enchanting tables, end portal frames, water, lava, and air causing agility bugs when falling or hurt which means that hitting a skeleton also causes glitches. I will edit my report on this bug. I created a new ticket that is related to this one, MC-105588
I have also confirmed this with illusioners.

Confirmed for Daylight Sensors
Confirmed 1.15.2
Confirmed for soul sand. This glitch could be a serious problem in the soul sand valley, as skeletons frequently spawn there.
Confirmed for piglins with crossbows.
Still happens in 20w09a.
This was fixed in 20w11a. The skeletons no longer have the speed issue, however, they still don't strafe on certain blocks. I made a report on the behavior without the super speed: MC-174500
this ticket is duplicated by MC-100588