When lighting (or blocks) update in some chunks, the lag is painfully laggy. In others, it is not. See the images below to see a sample of how high the delay is in one chunk vs. how low it was in others:
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Environment
Minecraft 1.14.x through the MultiMC launcher
macOS 10.14.4
No Resource Packs
Update:++ Disabling biome blending solved this, and reducing it reduced the spike. I still don't understand why lighting has any effect on biome blending