Hello, i have been working on a slime block elevator, then i noticed that the slime block did not retract (this happened on my Paper server). So i went to a 1.15.2 vanilla singleplayer world and tried it there -it worked (the sticky piston was facing north/south). I thought it was a paper bug, so i reported it on their Github (Issue #3539).

Then user "DoubleGe" noticed that in 1.15.2 vanilla singleplayer it works only if the sticky piston is facing north/south.

Then i tried it in 1.14.4 vanilla singleplayer world, it did not work on any direction.

Video (taken on 1.15.2 paper server): https://puu.sh/FVcFR/a312033aeb.mp4