This sample counts the number of entities loaded in all loaded chunks in all worlds. This counts players, items, frames, mobs, and even ender pearl signals. This is used to judge if the server is lagging because of entities or something else.

You are looking for a difference here. If you usually have 100-200 entities and it rockets up to 5 thousand, you may have a problem, however, this is usually taken care of by react.

Located at plugins/React/samplers/sample-entities.yml

component:
  # The interval at which this sample measures. 
  # You should not change this unless you know what you're doing.
  # This interval is sometimes highly sensitive to accuracy.
  interval: 100