Since I also tried passive M.2-to-SFF-8639 adapters with cables from Delock (that are labelled for PCIe Gen4) where the cable wires are directly soldered to the M.2 PCB traces but also throw PCIe Bus Errors (but at least very few) I’ve come to the conclusion that ANYTHING with copper cables and Gen4 or faster always needs an active component (if you’re out to get a configuration with 0 PCIe Bus Errors).
Even the best connector-plug connection (MCIO at this point in time) is worse for signal quality than a connection consisting of only a single wire.