Mobs move extremely slow, DoMobSpawning seems to be the cause

Whenever I set doMobSpawning to 'false', then spawn in a mob with commands, the mob appears to move incredibly slow when interacting with the player, specifically when the player hits it. The mob's movement will jump - it will be frozen for a second, then move again, then freeze for a second, then move.

Changing things like Render Distance, the number of mobs, max FPS, etc. does not have an effect; it is only the doMobSpawning gamerule.

I know that there were a few others stating similar issues, but those were marked as resolved for some reason. I am creating this one because the issue appears to still be there.