I’m very sorry that you are experiencing this issue. The real fix is the photo that josch posted above, with the yellow tape. Unfortunately we figured this out only after going with the ferrite solution, which turned out to be a red herring. The ferrite just made the FPC cable sit in a better position mechanically between the heatsink and module.
The real solution appears to be taping around the section of the FPC cable that is between module and heatsink (after the folded portion), because this will keep the cable a millimeter away from the heatsink and module. My theory is that this prevents the heatsink to become a ground plane for the differential signals that then abruptly ends where the cable exits the heatsink area.
In the meantime we have also respun the eDP adapter so that we can use a different cable that does not need the origami to flip it around. If you don’t want to try to apply the tape solution, please contact firstname.lastname@example.org and we will send you the new adapter + with tape preapplied.