https://bugs.freedesktop.org/show_bug.cgi?id=75491
--- Comment #8 from Eric Grüttefien freedesktop@donewell.de ---
Maybe they are too cheap and don't properly connect the ddc wires or pull the right pins down.
I've open one cable you seem be right. DDC alias AUX CH+/- seems not to be connected.
Cable Adaptor Detect alias Config 1 I' have still to check.
They are passive ones using a NPX/Phillips PTN3361B level shifter.
I will fix the cable and report back.
Thank you very much for the hint.