After inspection (my TimeFactor is no longer under warranty), I did not see anything really wrong, I just inserted a sheet of paper modeled on the metal / plastic sheet separating the two electronic plates.
This metal / plastic sheet is slightly conductive, and I feel that the loose connection came from there:
by powering the disassembled pedal in voluntarily supporting this sheet on the top electronic plate (the one on which are soldered potentiometers) I could cause the behavior of the pedal in the video.
Listed on the long term if the paper avoids these occasional madness of grain…
