Do certain actions, such as developing a fever, or cursing the religion (unintentionally), or eating suhoor after Fajr out of ignorance, invalidate the fasting for expiation of unintentional killing and require resuming the fasting anew?

Illness does not interrupt the continuous fasting of expiation. However, apostasy invalidates the fast and its continuity. If you utter words of apostasy while fully aware of what you are saying, then you must renew your faith and restart the fast. If the words were uttered unintentionally, then there is nothing upon you. Eating after Fajr out of ignorance of its dawn does not interrupt the continuity according to the Malikis, but that day is not counted from the two months, and you are required to make it up.