UI disappears after clicking 'Settings' button in VAB

[Gordon-Dry]

And this is spammed to the log afterwards:

KerbalEngineer -> Exception BuildAdvanced.Window() // System.NullReferenceException: Object reference not set to an instance of an object
  at KerbalEngineer.Flight.FlightAppLauncher.set_IsHoverActivated (System.Boolean value) [0x00005] in <134deb60e87843589b7ea1a020650b28>:0 
  at KerbalEngineer.Editor.BuildAdvanced.DrawSettings () [0x00374] in <134deb60e87843589b7ea1a020650b28>:0 
  at KerbalEngineer.Editor.BuildAdvanced.Window (System.Int32 windowId) [0x003d8] in <134deb60e87843589b7ea1a020650b28>:0  
(Filename: C:\buildslave\unity\build\Runtime/Export/Debug/Debug.bindings.h Line: 35)

KerbalEngineer ->   at KerbalEngineer.Flight.FlightAppLauncher.set_IsHoverActivated (System.Boolean value) [0x00005] in <134deb60e87843589b7ea1a020650b28>:0 
  at KerbalEngineer.Editor.BuildAdvanced.DrawSettings () [0x00374] in <134deb60e87843589b7ea1a020650b28>:0 
  at KerbalEngineer.Editor.BuildAdvanced.Window (System.Int32 windowId) [0x003d8] in <134deb60e87843589b7ea1a020650b28>:0  
(Filename: C:\buildslave\unity\build\Runtime/Export/Debug/Debug.bindings.h Line: 35)

Those two files are altered as well:
GameData\KerbalEngineer\Settings\BuildAdvanced.xml
difference (left is after the issue occured, right is as it was before):

GameData\KerbalEngineer\Settings\SectionLibrary.xml
difference:
several "LineCount" entries are changed, even of UIs which are not available in VAB.

Reminder:
This is NOT because of me setting GeneralSettings.xml to read-only, it always happens.
(see #84 )

Log:
KSP logs 2021-12-20-02.zip