Affects 1.18.12 (Bedrock/Windows)
I found the source of the issue: there were too many cows above the clime chunks. After "removing" some of the herd, slime did spawn below again.
Case closed.
If an update breaks compatibility, it should not be run on that hardware. I am hoping for a roll back and then maybe announce end of support.
Still present in 1.19.2
I realize this bug is not game breaking, but it has been a year since it was first reported. Please fix, or at least give a status update.