Final Hour - S4-E6
Corrected entry: In the last episode after Cameron travels forward in time, Kagame says he remembers Liber8 from Uncle Julian's stories of when he was younger, indicating that Cameron et. al were successful in changing the present. Then at the fountain scene she sees her son. When current (aka old) Alec holds her back, the immediate assumption is that the time change also changed who Cameron's son's mother was. But then Alec explains that everyone thought she died the day of the accident at the execution, insinuating that Cameron's husband remarried and that this woman was Cameron's son's step-mom. The plot hole exists in that if there was no modern Liber8 there would not have been an execution or accident (time travel) in the first place, so there would be no reason for anyone to think Cameron had died. In fact, had she been successful and managed to come back at essentially the same day/time as she left, no one other than Alec would have known she left since it would not have seemed that she was gone at all.
Correction: You've misunderstood everything Alec tells Kiera. Alec said they (Alec, Carlos, etc) thought Kiera died the day they sent her to the future, he was not talking about the explosion during the execution. Alec, Carlos, and Julian then dedicated themselves to making a better world. There ended up being no corporate congress and no terrorist organization. Liber8 didn't exist in the future (and this Kagame we see was never a terrorist) and there was never an execution or explosion. The woman Kiera sees with her son is Kiera herself, but an alternative timeline Kiera who was born into the new, more peaceful world who never joined the military or CPS (since it was never created). Alec stops Kiera from seeing her son since his mother never died. While one can argue the whole paradox of the situation, it's beyond the scope of a plot hole since time travel into the past isn't real and we don't know what would happen, and the show already showed that altering the past doesn't directly effect people from the future who are in the past when Matthew Kellog's grandmother was killed.
Bishop73