Direct answer
Mob pathfinding cost is driven by active AI decisions and path recalculation, not simply the number of monsters on the server.
How to check it
- Compare idle mobs against mobs repeatedly chasing targets, avoiding obstacles or recalculating routes.
- Run a spark profile during the pathfinding-heavy event and identify AI/navigation branches.
- Look for constantly changing blocks, doors or target locations that repeatedly invalidate paths.
Example: A mob chasing a player through constantly closing doors can recalculate paths repeatedly; the same mob sitting in a clear pen is not a comparable AI workload.
What to change
Simplify unnecessary obstacle mazes or move decorative mobs into a design that does not require constant pathfinding. Tune platform-specific AI settings only after validating compatibility.
Software and version notes
Paper has a pathfinding-on-block-update option that can change behavior around automated builds. Folia and alternative forks have different scheduling and setting availability.
Verify the result
Run the same AI scenario and verify mobs still navigate, attack or flee correctly while tick cost declines.