Direct answer
A busy cluster of players, mobs or redstone can keep one Folia region behind while other, independent regions run smoothly. More tick threads do not make a single heavily loaded region run in parallel.
How to check it
- Reproduce the lag with the same group of players in one location, then spread test players into distant independent areas. Note whether the issue is local.
- Use the profiling and tick diagnostics supported by your Folia build; inspect region-local work such as entities, plugin callbacks, chunk loads and redstone.
- Record physical CPU availability and whether the tick pool is fully occupied; do not mistake one hot region for overall CPU saturation.
What to change
- Reduce the measured workload in the affected area: expensive AI, rapidly updating blocks, plugin tasks or player-driven chunk loads.
- Retest with the same workload before tuning threaded-regions.threads. A region performing too much work on one tick will not necessarily improve by adding threads.
Software and version notes
Compatibility and safety
Folia regions merge and split dynamically. They are not fixed per-player chunks, so measuring only a global average can conceal one unhealthy region. Do not run Paper-only profilers that assume a single main thread without checking Folia support.
Verify the result
Reproduce the original hotspot and compare local tick performance, server-wide CPU headroom and any gameplay side effects.