When I try to load the saved game file with the issue, it crashes immediately now
I told you above

But strange that you don't get more error messages

Only suggestion would be to start a new game with the .dll, and hope that the error appears again

When I try to load the saved game file with the issue, it crashes immediately now
Proves, that it's a graphical problem.
If there's no CvGameCoreDll in the assets folder of your mod, then put the attached debug dll into there (it's not mine, phungus compiled it, but i can't find the thread). If you then play in windowed mode, you should get some more exceptions on startup, which should tell you where the problem is (but you can't play the savegame with that .dll, you'll have to take it out again before further playing).
Thanks
I do have a couple of questions regarding the messages. Is there a thread that explains the different expressions.