TimeUS param stopping recording early in flight

I am running a Pixhawk 2.4.8 on a quad, and I need the TimeUS param for some flight time tests that I am doing. I have done two flights where, when I reviewed the log file, the TimeUS parameter didn’t log until disarm and instead stopped at around 12-13 minutes. Is there a setting that can change this, or is there another param that gives time? In this log I flew for ~29 minutes, but the TimeUS param stops at about 13 mins: https://drive.google.com/open?id=1aZ7F9SlsmOBxsEYsMR4XQDiWpwnhzTek.