TL/DR: author tried to run RS485 cable next to 1000V DC line, could not solve EMI issues, did no real diagnostic (except cable swap), gave up and went to analog.

Also tons of AI-generated slop. Fr example the "shields do not protect from capacitive coupling" part is absolutely nonsense. Ground reference jumping, within reason, is totally OK for RS485. The disturbances do not accumulate. While DC/DC converters _do_ have fast switching transients, those are blocked by input/output capacitors and do not appear on the cables, unless those converts are defective.

Also, the title seems to lie. Author tried original cable and one more "OEM cable", and that's it.

Worst kind of AI slop.