Only some vague speculation, as they didn’t go into much detail on the webcast. “Out-of-family data error” could have been a faulty sensor. Some of the mission control callouts referred to “bleed valves”, and “LOX top-up”, which could suggest an issue with the LOX pressurization system, either on the rocket or with the ground support equipment. Though this also could have just been to counteract boiloff as the rocket sat on the pad while they worked on a problem with different system. Again, just speculation on my part.