I could experiment myself.
I have limited Windows experience, but I do have Microsoft Remote Desktop and access to some Windows systems at work (not via Citrix, just directly to the Windows systems). I mostly have to use Windows to take some mandatory training courses that are written only for Windows, otherwise I spend most of my time working with Linux/Unix systems at work.
But if you can explain how I would use the "Insert" key, and how it should behave when I use it (I really am that Windows ignorant 🙂), on some commonly available Windows app (Notepad, Firefox, Thunderbird, Internet Explorer, etc....), I could experiment a little and see if I can come up with something, or some Karabiner setting that works.
It is even possible, I'll succeed where you fail, and that might indicate a difference because of Critix (anything different in the setup is a possible cause of interference, so it can also be a useful diagnostic).
I can't promise anything, but I'm sure I can spend a little time this weekend (after vacuuming the house 🙂 ).