[MC-149553] Slime chunks not working in 1.14

Slime chunks do not spawn slimes. I have run an experiment over 200 chunks, none spawn slimes.

Environment

OS: macos High Sierra, Java: 10

Does this still happen in 1.14.1 Pre-Release 2?

Still a problem in 1.15 pre-release 3
No slimes spawn in the world at all.

Used commands to kill everything except for slimes and player, repeatedly. But still no slimes show up.