So both crashes appear to occur at the start of the human turn after updating AI strategies (CvPlayerAI::AI_getStrategyHash). But a lot of things could still happen, silently, in the DLL before the crash occurs; and it's not easy to tell when exactly the strategy update happens – because it's a cache that gets updated on demand. It might be feasible to narrow down the cause by inserting additional logging code, but, since you're able to compile a debug DLL, it should be much quicker for you to reproduce the crash with a debug DLL and the debugger attached (
screenshot showing the config for that in VS). That should result in a break at the line of code (probably in the DLL) that causes the crash with the Call Stack window showing the function calls that lead there. Should only debug in windowed mode to avoid a freeze when a breakpoint is hit.