The waveform disappearing seems to be linked to the acquisition speed (SPS). At 5:20, you go into the Acquire menu, and on "Normal" horizontal resolution, you're pulling 10MSPS (look at the bottom right), and it has a display, and then "Fast" is 500kSPS, which doesn't have a display. At 5:25 you increase sample rate to 5MSPS (10us/div @ "Fast") and that has a display again.
At 5:54 it works on "Normal" down to 5MSPS (200us/div @ "Normal"), then dies below that.
I'd guess that something changes mode below 5MSPS.