Basically, the small map in the right bottom corner only shows the cultural borders and the individual units exploring, not the explored terrain. However, only a thick strip of the map remains black, the rest is normal (on the left in the screenshot). This only happens to the first player out of two, although the second one can also come across such a black strip later on (I'm not sure, it might be the same as that of the first one).
How to deal with this bug?
How to deal with this bug?
Spoiler :
