On our server, I've found that enabling the following option causes huge delays when players are processing blocks in bulk.

# config/modernfix-mixins.properties
mixin.perf.cache_blockstate_cache_arrays=true # default
mixin.perf.cache_upgraded_structures=true  # default

Among them, cache_blockstate_cache_arrays has the most significant impact. Analysis from Spark indicates that approximately 20% of tick time is spent processing cache information.

Due to many mods in ATM9 provide the ability to process a large number of chunks, I believe this option should be disabled by default.