Got a CTD in the Simulator mission "Hornet's Nest" (albeit the modfied one from Timid's Content Unlocking Missions, v1.12), that does not occur when Realistic Combat is disabled:
Bummer! I have followed your steps but can't reproduce this bug. 
Can you?
Pared down my mod list to just Realistic Combat 1.22.1, GraphicsLib 1.6.1, MagicLib 0.42.1, LazyLib 2.7b, Content Unlocking Missions 1.12 and SpeedUp 0.7.2...
Also deleted the entire \saves\missions folder and sub-folders (where all saved mission .variant(s) are stored, so stock loadouts; same changes to Radar.json and Toggles.json.
Still got the exact same CTD, though at different points throughout the battle (the CTD won't happen right away); disabling Realistic Combat allows Hornet's Nest to be completed.
I think I'm having similar issues. Game crashing and throwing up the error about fatal null exception. I thought it was mods conflicting but after reading this section. I disabled all mods to just only realistic combat enabled and tried to play the missions, the second mission or so involving more ships seems to throw more chance to crash the game. Not only that issue, in my modded campaign gameplay getting into any kind of battles will crash. Since I been playing with realistic combat mod before the hot-fix to resolve the allies spamming, there was no crashing null pointer like that. I did not modify the realistic combat as all settings are default out of the box, except the part that enable this mod to run.
I assume this is relevant section of starsector log before the crash. not much difference from other report except that last says unknown.
72120 [Thread-9] INFO sound.public - Creating streaming player for music with id [miscallenous_main_menu.ogg]
72121 [Thread-9] INFO sound.OooO - Playing music with id [miscallenous_main_menu.ogg]
80709 [Thread-7] INFO sound.public - Cleaning up music with id [miscallenous_main_menu.ogg]
81129 [Thread-9] INFO sound.public - Creating streaming player for music with id [battle_ambience_01.ogg]
81130 [Thread-9] INFO sound.OooO - Playing music with id [battle_ambience_01.ogg]
102994 [Thread-7] INFO sound.public - Cleaning up music with id [battle_ambience_01.ogg]
103154 [Thread-9] INFO sound.public - Creating streaming player for music with id [miscallenous_main_menu.ogg]
103155 [Thread-9] INFO sound.OooO - Playing music with id [miscallenous_main_menu.ogg]
106312 [Thread-7] INFO sound.public - Cleaning up music with id [miscallenous_main_menu.ogg]
106657 [Thread-9] INFO sound.public - Creating streaming player for music with id [battle_ambience_01.ogg]
106658 [Thread-9] INFO sound.OooO - Playing music with id [battle_ambience_01.ogg]
115064 [Thread-7] INFO sound.public - Cleaning up music with id [battle_ambience_01.ogg]
115167 [Thread-9] INFO sound.public - Creating streaming player for music with id [battle_ambience_01.ogg]
115168 [Thread-9] INFO sound.OooO - Playing music with id [battle_ambience_01.ogg]
115211 [Thread-3] ERROR com.fs.starfarer.combat.CombatMain - java.lang.NullPointerException
java.lang.NullPointerException
at listeners.Retreat.advance(Retreat.java:114)
at com.fs.starfarer.combat.entities.Ship.advance(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.o00000(Unknown Source)
at com.fs.starfarer.StarfarerLauncher$1.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
