Mega Charizard X

it's still can be reproduced, though the new changes to fish spawning does help slightly with retaining the server's performance

yes it's present in 1.15.2

can confirm in 20w09a

Yes it's method has just been changed, just requires the pistons to support it from not getting put into entity state completely.

probably best state your hardware and settings for further details to help define the issue c:

Paper has a inbuilt plugin to kill passive mobs if they cause too much lag, so putting multiple sheep in the same block cell will cause entity collision which is able to cause lag and paper will kill it, I had such reproduced on 1 I played on

it's still on a block, do F3+B to see the hit box, the horse doesn't require the front body to be specifically on the grass block to eat, it's hit box dependant on where the hit box is standing on.