A world-generation feature is writing outside its chunk
What it looks like in your log
Detected setBlock in a far chunk [15, 7], pos: BlockPos{x=250, y=64, z=120}, status: minecraft:featuresWhat causes it
Minecraft logs this every time a placed feature sets blocks in a chunk it does not own. The mod or datapack that defines the feature has a bug in its size or placement. Each line is a lock contention and a slow chunk, and enough of them look like lag while new terrain generates.
How to fix it
Update the mod or datapack that provides the feature, or if it is your own datapack shrink the feature so it stays within its chunk. It is not world corruption and the server is safe to keep running; it just generates slowly.
Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.
Check your own log