Is it obligatory to make up past prayers due to not washing the ankles during ablution, out of ignorance of the ruling, knowing that there was a subsequent doubt about the matter, and a lack of immediate research into it, in addition to the differing opinions of scholars regarding the obligation of making them up?

Washing the ankles is obligatory in ablution according to the general body of scholars. For one who omits it out of ignorance, the view of the majority is that he must make up the missed prayers, and this is the more cautious approach. It is especially emphasized for the questioner to inquire, given his doubt. As for prayers intentionally omitted, the fatwa (definition) we adopt is that making them up is likewise obligatory, and this is the view of the majority.