Remember the classic episode of Star Trek: The Next Generation called “Cause and Effect?”
In it the Enterprise and her crew are caught in an endless causality loop, where it repeats the same day over and over. The day always ends with the ship being destroyed in an accident with the U.S.S. Bozeman, which had come from decades in the past via a time portal.
Long story short, the crew eventually realizes what was happening and finds a way to break out of the loop.
(It’s such a good episode.)
For the story in Heroes Reborn, “June 13th, Part 2” was the closing of such a loop.