Martin_Hasenberg

@Thilo: So, I did a little more testing (I suppose it would perhaps be a different issue, but the result is negative anyway), which confirmed my second assumption in my first comment: In 1.14.4 and 1.15 items and xp-orbs that are positioned on a slime block's edge, with part of the hitbox on top of an air block, are bounced up. No change there. Conversely, if there is an ice block instead of air, items just keep sitting on the blocks, same in 1.14.4 and 1.15 (the latter I checked for xp-orbs only in 1.15, because I couldn't figure out a way to place them on the edge and also move other blocks up with the slime blocks in 1.14.4 [don't know much about commands and such]).

Renaming this issue seems like a good idea to me too.

I think that 1. the problem is better put as: the item is not bounced into the air,  2. this is not caused by the position of the item on the slime block itself but by the item's hitbox's position partially above the ice block (if the item was to slide all the way to the obsidian, it would bounce).

What I can tell about the change from testing in creative (aside from my trusty snocrash gold/xp farm not working anymore in 1.15): in 1.14.4 items, or, in my case experience orbs, slid further above the slime block.

I attached screenshots of the test scenario, hoping that they might explain what has changed between 1.14.4 and 1.15.