Does ablution become void upon feeling something exit during prayer after relieving oneself and performing istinja, and what should one do about past prayers in which the same feeling occurred without redoing ablution?

If your feeling of something exiting is merely a doubt, do not invalidate your prayer but continue with it, for the Prophet, peace and blessings be upon him, said: "He should not leave until he hears a sound or finds a smell." However, if you are certain that something exited, then your ablution is nullified, your prayer is invalidated, and you must remove the impurity, perform istinja' (washing private parts), make wudu' (ablution), and repeat the prayer. If you did not do so, then determine the number of prayers during which this occurred and make them up, because they are a debt upon you.