The new spawning algorithm in 1.14 stops at chunk borders. This leads to mob spawning being clustered in the center of chunks instead of being evenly distributed throughout the world, like in previous version.
Since the stated goal was to replicate 1.13 mob spawning as close as possible and this is a major change, which negatively effects mob distribution, this can only be seen as a bug.
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violine1101
violine1101
This bug was showcased in this video by @unknown: https://www.youtube.com/watch?v=3ZEY-lWgfdc
LogicalGeekBoy
I can confirm. I tested a mob farm in 1.13.2 and also in 1.14 and saw a 30% reduction in rates. This was confirmed by SciCraft code analysis which Gnembon mentioned in his video above. The change to the algorithm is related to pack-spawning. If any mob in the pack would spawn in a different chunk from the origin then the whole pack is aborted and hence the reduction in mob spawns generally.
violine1101
Can confirm as well. In a void test world with biome changed to "plains", I was able to observe that on the 16×16 platform that did not cross chunk corners, there spawned roughly three times as many mobs as on the 16×16 platform that was placed exactly where four chunks meet.
LogicalGeekBoy
I've done a follow up test and this behaviour is still the same in 1.14.1-pre1. Thanks for looking into it <3
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coschevi
Might be related to / causing MC-147890?