Can't exit buildings / activate flights

[GTHvidsten]

KSP has now started doing this more and more often. Suddenly I cant activate a flight, or exit a building. I've tried disabling my plugins, one by one, to see if any of those are causing it, but they are not.
With my current save it happens constantly when entering the Astronaut Complex, but also happens if I try to terminate a flight.

I've previously seen this problem occuring on these forums, all the way back to 2014, so I'm surprised this hasn't been fixed 3 years later! Seeing as the log file also has many NullReferenceExceptions, this is really a sign of sloppy programming/testing.

I'm sure it can be fixed by editing my savefile, somehow, but the fixes I've seen has to do with deactivated astronauts, and they're 2 years old, so I'm not even sure they apply to 1.2.2.
The problem also occurs in Tracking Station, which is an altogether different building than the Astronaut Complex.
What can I try to do to my savefile so that the game starts working again?

[GTHvidsten]

I tried the suggestions in this thread:

but it didn't work. I also tried some of the suggestions in the answers to the thread, but none of those worked either

 

This appears in output_log.txt when I try to exit the Astronaut Complex:

Quote

Flight State Captured
 
(Filename: C:/buildslave/unity/build/artifacts/generated/common/runtime/UnityEngineDebugBindings.gen.cpp Line: 42)

Exception handling event onGUIAstronautComplexDespawn in class ACSceneSpawner:System.NullReferenceException: Object reference not set to an instance of an object
  at KerbalRoster.ValidateAssignments (.Game st) [0x00000] in <filename unknown>:0 
  at Game.Updated () [0x00000] in <filename unknown>:0 
  at GamePersistence.SaveGame (System.String saveFileName, System.String saveFolder, SaveMode saveMode) [0x00000] in <filename unknown>:0 
  at KSP.UI.Screens.ACSceneSpawner.onACDespawn () [0x00000] in <filename unknown>:0 
  at EventVoid.Fire () [0x00000] in <filename unknown>:0 
 
(Filename: C:/buildslave/unity/build/artifacts/generated/common/runtime/UnityEngineDebugBindings.gen.cpp Line: 42)

NullReferenceException: Object reference not set to an instance of an object
  at KerbalRoster.ValidateAssignments (.Game st) [0x00000] in <filename unknown>:0 
  at Game.Updated () [0x00000] in <filename unknown>:0 
  at GamePersistence.SaveGame (System.String saveFileName, System.String saveFolder, SaveMode saveMode) [0x00000] in <filename unknown>:0 
  at KSP.UI.Screens.ACSceneSpawner.onACDespawn () [0x00000] in <filename unknown>:0 
  at EventVoid.Fire () [0x00000] in <filename unknown>:0 
UnityEngine.DebugLogHandler:Internal_LogException(Exception, Object)
UnityEngine.DebugLogHandler:LogException(Exception, Object)
UnityEngine.Logger:LogException(Exception, Object)
UnityEngine.Debug:LogException(Exception)
EventVoid:Fire()
KSP.UI.Screens.ACSceneDespawner:BtnExit()
UnityEngine.Events.InvokableCall:Invoke(Object[])
UnityEngine.Events.InvokableCallList:Invoke(Object[])
UnityEngine.Events.UnityEventBase:Invoke(Object[])
UnityEngine.Events.UnityEvent:Invoke()
UnityEngine.UI.Button:Press()
UnityEngine.UI.Button:OnPointerClick(PointerEventData)
UnityEngine.EventSystems.ExecuteEvents:Execute(IPointerClickHandler, BaseEventData)
UnityEngine.EventSystems.ExecuteEvents:Execute(GameObject, BaseEventData, EventFunction`1)
UnityEngine.EventSystems.StandaloneInputModule:ProcessMousePress(MouseButtonEventData)
UnityEngine.EventSystems.StandaloneInputModule:ProcessMouseEvent(Int32)
UnityEngine.EventSystems.StandaloneInputModule:ProcessMouseEvent()
UnityEngine.EventSystems.StandaloneInputModule:Process()
UnityEngine.EventSystems.EventSystem:Update()