They reported a loss of telemetry during or right after the reentry burn. Precisely what happened from there hasn't been specified yet but it was likely an RUD starting around the time the feed from the booster went wonky. You might have seen the speed and altitude were updating randomly for a few seconds after the video froze so it wasn't all at once. That *could* indicate it was out of control.
A lot of things can do it at that point in flight. An engine failure on relight, loss of aerodynamic control, or breakup on reentry, just as a few examples.