I have noticed this off and on with other things, but most prominent this evening.
`Fetching packet for removed entity class_1542['Air'/225347, l='ServerLevel[world]', x=-500.20, y=134.00, z=-2199.80]`
At that location, we had about 30 chickens all stacked on top of each other for our egg farm. Breaking the containing blocks and letting the chickens go free resolved the warnings at that location. I am inclined to agree that it is related to mob cramping.
This seems to also occur when using the nether to travel and going back into the overworld at a different location. The server times out "Tick took 60 seconds, assuming server crashed" and restarts. This continues to happen until the player that traveled returns to the nether.
thanks
Confirmed this is happening to me as well on version 1.17.30