What is the ruling on repeated masturbation while fasting for expiation, and is it necessary to resume the fast anew?

What you did, having intercourse in Ramadan (definition), is a great abomination and a major sin. It necessitates making up the day along with expiation (kaffarah (definition)), which is: freeing a slave; if you cannot find one, then fasting for two consecutive months; if you are unable to do that, then feeding sixty poor people. Masturbation is forbidden and invalidates the fast, but it does not necessitate expiation (kaffarah); however, it breaks the continuity of the obligatory fasting.

You must repent to Allah Almighty and fast for another two consecutive months as expiation for masturbation. Know that the door of repentance is open.