Maps visual - Municipality isn't recognized

I'm working on a BI that includes a Filled Map visual.

One of the municipalities I'm trying to paint is Maia, in Northern Portugal, with colour based on a numeric variable, but it is the only munucipality that is greyed out in the map. I've double checked that the variable isn't NA or 0, so it should be coloured. What's more, if I change the app language from Portuguese (Portugal) to English (U.S.A.), even less municipalities are painted.

I've left an image below that shows the issue.

Is there some way to solve this or is it a BI issue?