It’s because of entity’s you see when tnt isnt ignited it is stored as NPC data which wont lag out easily, once ignited it turns into entity, or more specifically 5. Tnt is stored as 5 entity’s which is the minimum of entity’s stored in a 1x1x2 hole that will explode. 5 tnt blocks lags a little because its stored as 15 entity’s being loaded at once.
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