Just thinking out loud... Could be the electrical switch that activates the clutch cutout. I dunno all the circuits involved in that but on my
old 580D the switch came loose on the shuttle and she stopped cold. Tightened it back up and it pushed it's detent ball back in the case and everything was fine.
The super L uses a different trans than my D but it has a cutout
for loading and shifting too.
Could be a chaffed wire or flakey switch activating the cutout.
Just an Idea...