After doing some library work, I have managed to make my KiCad crash. I am about to reinstall KiCad to see if that fixes it, but I thought I would hold off on that in case there might be some useful information for the devs.
The main application opens, I can create new / open existing projects, I can open schematics, but as soon as I want to add a symbol to the schematic (and the libraries are being attempted to load) - depending on some ‘things’ I did, see below - the application crashed with either a ‘attempt to write at memory address error’ (didn’t get a screenshot of that one), no error at all, or an ‘invalid project file’ error.
Note the cut-off path. The full path for this project is:
D:\Sync\Sync - Projects\PRJ-ZZZ - KiCad Simulation\PRJ-ZZZ - KiCad Simulation.kicad_pro
I currently have no symbol libraries in my symbol library table for debugging purposes, but it still crashes. As I managed to break my KiCad after doing some library work, I thought I would start looking for clues there as everything worked normally before.
All I can describe with respect to what I’ve done to end up in this mess is the following.
[ Stable situation ]
Add the ‘pspice.lib’ and ‘Simulation_SPICE.lib’ symbol libraries to my library table.
[ Oh wait, I have to note this down - These libraries are from the official symbol libraries, but they are an older format: .lib vs .kicad_sym ], might be a clue…
Create a new symbol library for personal use, copy required symbols from the aforementioned libraries to my own library.
Create a new project so I can do some simulation work with my new symbols in my new library.
[ Arrived at unstable situation ]
Now I came to the point where KiCad would either crash without any error windows, or the ‘attempted to write at memory address error’, or the ‘invalid project file error’.
I can’t remember the exact combination, but it was combinations of toggling the ‘active’ checkbox for the pspice.lib / Simulation_SPICE.lib / mylibrary.kicad_sym, and deleting the library entries which caused me to ‘toggle’ between the different errors/crashes.
Any other info I can provide? Any ideas how I can further pinpoint where this problem is coming from? I will hold off on reinstalling KiCad. If anything, I feel like the cut-off path from the error message is useful to fix, at least.
Thanks for any input 
Version info: Application: KiCad (64-bit)
Version: (6.99.0-2202-g8f1b2acdc6), release build
Libraries:
wxWidgets 3.1.7
FreeType 2.11.1
HarfBuzz 4.2.0
FontConfig 2.14.0
libcurl/7.83.1-DEV Schannel zlib/1.2.12
Platform: Windows 10 (build 19044), 64-bit edition, 64 bit, Little endian, wxMSW
Build Info:
Date: Jun 21 2022 09:41:36
wxWidgets: 3.1.7 (wchar_t,wx containers)
Boost: 1.79.0
OCC: 7.6.0
Curl: 7.83.1-DEV
ngspice: 37
Compiler: Visual C++ 1929 without C++ ABI
Build settings:
KICAD_USE_OCC=ON
KICAD_SPICE=ON
but 7zip did the trick).