Direct answer
Sand/gravel avalanches and TNT-like block physics can spawn many short-lived falling-block entities at once; this may create bursty physics updates.
How to check it
- Observe the event causing the spike and note whether it involves gravity blocks, large WorldEdit operations or custom falling-block effects.
- Collect a spark trace during the falling-block burst and separate one-time placement cost from a repeating command loop.
- Check for plugin-spawned displays that only look like falling blocks, because their lifecycle and API differ.
Example: One avalanche of sand may cause a brief spike; a command repeatedly summoning falling blocks can create persistent load. Record whether the event is isolated or self-repeating.
What to change
Break up large, simultaneous gravity-block operations; schedule decorative effects in smaller batches or use display features where appropriate and supported.
Software and version notes
Never issue broad /kill @e cleanup commands on a production world. Gravity-block behavior is part of farms and redstone builds; test any optimizations first.
Verify the result
Confirm the intended structures settle correctly with no missing blocks and compare peak tick time across matched events.