Slimes not spawning in slime chunk

Tried building a slime farm in a regular world based on a slime chunk using my seed & chunkbase.com. After a long time of no slimes, I checked the supposed slime chunk in 1.19.2, 1.18.2, & 1.17.1 without any success. Either I'm doing something wrong or the public information about slime chunks is wrong.

Seed: -6287945046413747899

Chunk: (-288, 30, -160) to (-273, 30, -145)

According to https://www.chunkbase.com/apps/slime-finder#-6287945046413747899 and according to https://www.online-java.com/5JEe1zHsNP (using the supposed code snippet for calculating slime chunks from the wiki https://minecraft.fandom.com/wiki/Slime#Java_Edition ) this is a slime chunk and slimes should spawn, regardless of light level, below level 40.

Testing:

Created a new superflat world with the following settings (all other settings should be left as default - eg difficulty should be Normal):

1. Remove all layers from superflat (so that it's just air)

2. Set seed as above

3. Turn off "generate structures"

4. Set gamemode to Creative

5. Click "Create World"

Upon joining the world:

1. Double-tap space to make sure you don't die in the void

2. Run 

   /tp @p -288 30 -160

1. Run 

   /fill -288 29 -160 -273 29 -145 minecraft:glowstone

1. If desired, re-run the above command many times with varying Y-levels of depth

2. Over time, observe that no slimes spawn in this supposed "slime chunk"