Very often, I'll crash when using the Pocket Gust's ship system (Assume Wing Control) from Diable Avionics, and starsector.log shows this at the very bottom.
Spoiler
761917 [Thread-4] ERROR com.fs.starfarer.combat.CombatMain - java.lang.NullPointerException
java.lang.NullPointerException
at data.scripts.WeaponArcsPlugin.advance(WeaponArcsPlugin.java:89)
at com.fs.starfarer.title.Object.float$Oo.o00000(Unknown Source)
at com.fs.starfarer.combat.oOOO.B.super(Unknown Source)
at com.fs.starfarer.combat.CombatEngine.advanceInner(Unknown Source)
at com.fs.starfarer.combat.CombatEngine.advance(Unknown Source)
at com.fs.starfarer.combat.CombatState.traverse(Unknown Source)
at com.fs.state.AppDriver.begin(Unknown Source)
at com.fs.starfarer.combat.CombatMain.main(Unknown Source)
at com.fs.starfarer.StarfarerLauncher$1.run(Unknown Source)
at java.lang.Thread.run(Unknown Source
I tested this on a brand new campaign, without displaying any additional weapon groups, and it didn't crash in the simulator, but it did when in a real battle.
I've had it crash inside the simulator before, though, but I don't know if I was displaying weapon groups at the time.