there is a prefab in the game that when spawned, lags the game. the prefab is "fireball_projectile". it is something from the forge that stayed in the game. you can use the console to spawn it:
. when spawned, it starts draining your fps. it takes about a minute to become noticeable.
this bug in general does not affect the game much because it is normally impossible to do without the use of specific console commands. but it is a really interesting bug.
this is impossible to pull off without using console. type c_spawn("fireball_projectile") into remote console. wait about 1 or 2 minutes.