I've been trying to figure this out for weeks and it is driving me nuts! Whenever coal or uranium is discovered, the province switches to unknown and then generates a new trade good the beginning of the following month. It isn't an event (I was in debug mode to see). It isn't related to the trigger because I met those and then I deleted them to test it. The province has the trade good displayed until the end of the month and then boom it is gone. I don't have any DLC, but the Elysia mod has coal and doesn't have this issue for me. I even checked that code and it seems identical. Is this a bug or am I missing something?