When an entity is created, has a score set, and is then killed, all within the same tick, its score remains on the scoreboard. This causes scoreboard.dat to become abnormally large, causing extreme lag when saving. This happens most consistently when the above happens through a function that is (directly or indirectly) run from minecraft:tick, but also seems to happen through other methods of executing functions (although I cannot reliably reproduce this).

To reproduce:

1. Make a new world
2. Add the attached datapack
3. Verify that there are no entities on the scoreboard by running: scoreboard players list
4. Run: scoreboard objectives add foo dummy
5. Verify that the scoreboard rapidly grows in size by running "scoreboard players list" a few times