Did you wait till the nightfall started it's 30 second timeout at the end, or did you quit to orbit right after the chest opened? Cause this particular nightfall is kind of odd. The completion and any weekly rewards won't register before long after the chest has opened. I've fallen victim for this myself several times, by being hasty and leaving too soon, after picking up the chest rewards. But as it turns out, I've aborted before completion.

If it’s your 145k Insight Terminus run, then it’s listed as a DNF. Most likely because the leader left for orbit before mission completion showed on screen.

Between defeating the boss and when the chest opens at the end of the strike the timer does not stop. If your timer is past 15 minutes, your score will decay. It's possible that your score decayed below 100k while you were waiting for the chest to spawn.