If your ancestor acquired another citizenship before October 3, 1981, the date from which Portugal began allowing dual citizenship, they may have lost their Portuguese nationality. In that case, the line of transmission could be interrupted, unless you (or your parent, if the ancestor is your grandparent) were born before that acquisition, that is, while your ancestor was still Portuguese.
That is why it is so important to know the exact date your ancestor obtained that other citizenship. If you don’t know it yet, we invite you to look into it and take this assessment again. EuroPassport also offers a genealogy service that can help you find this information. We’ll be happy to guide you through the process!