Upstream has released updates that appears to apply and compile correctly.
This update has not been tested by PaperMC and as with ANY update, please do your own testing
CraftBukkit Changes:
7033f180 Hoist out synchronisation from ChunkRegionLoader
Spigot Changes:
500ff5d4 Rebuild patches
Additional Paper changes:
Fixed Versioned World Folders to not synchronize on ChunkRegionLoader
Optimized Save Queue even more to use a Long2ObjectOpenHashmap for save map
Add World#getXIfLoaded to IWorldReader to expose it to more places
6711724fae