When entering a biome which has a lot of bamboo, and a lot of regolith grass (seen it in the bamboo jungle biome), the bamboo immidiately starts popping out of the regolith and breaks the whole column of bamboo. This causes a lot of lag - from the breaking and the items.

In the picture all the blue dots on the map are items - bamboo. And theyre not done breaking yet.

Minecraft 1.16.5, unearthed 1.1.2b.