The file being from a different mod is still a massive hassle though, since it cannot just be opened by DoC. I tried installing the mod following the instructions in the download link but then I ran into a failed to uncompress game data error.
Can you still open those saves yourself and tell me about the city positions and culture values of those cities, so I can reproduce the situation using the WB?
Sorry it took so long for me to reply to this.
There are three cities that could be relevant:
Qurtubah in its default location, on that river plains with a hill to the south, a crab to the southwest, Wine to the east and Sheep to the northeast, Moorish controlled.
Madrid also in its default location, 3 north 1 east of Qurtubah, Spanish controlled.
Barcelona also in its default location, 3 east of Madrid.
Situation in the first savegame, 950AD/Turn35 ingame/Turn216 according to the name of the autosave:
Culture in Qurtubah: 74
Culture in Madrid: 100
Culture in Barcelona: 21
The hill 2 east of Qurtubah is 100% Moorish, the hill 1 northeast of it where the first fort will be built is onowned.
Situation in the second savegame, 1030AD/Turn43 ingame/Turn224 according to the name of the autosave:
Culture in Qurtubah: 98
Culture in Madrid: 163
Culture in Barcelona: 37
At the start of the turn the hill 2 east of Qurtubah is 100% Moorish, the hill 1 northeast of it has a Spanish controlled fort with 91% Spanish, 4% Moorish and 4% Independent culture. Upon replacing the fort with a mine the southwestern hill suddenly becomes neutral instead of being Moorish controlled.
From what I can remember building a fort on that now uncontrolled tile switches ownership of it over to the Moors and immediately evicts the workers who built it.
Hope this could help.