It took them that long to figure this out? When I got my X1C (6th gen, so more than a year ago) I immediately saw that there is something fishy with TB - none of my long, active TB cables worked, eGPU would get into connect/disconnect cycle. Only short, passive cables was working. I even went to Lenovo website and they removed all long TB cables from sale leaving only the short ones - the active one was still visible in google search. They knew about this for over a year, so I'm not sure about that statement that the issue appears after 6-12 months of use. How can a software problem manifest itself after prolonged use?
I'm surprised the X1E / P1's are not on that list.
My X1E isn't part of the list but I've had a handful of oddities related to USB-C such as connections dropping as noted by the link above. My TB experience however has been positive, I have the EGPU set up and its been working largely problem free, so X1E may indeed not need it