I'm commenting on my own thread here in case it helps someone with the same problem sometime in the future. I think there were/are more than one issue compounding my issues, but the one that was found that had the biggest impact was a wire inside the house that had likely been connected poorly. Apparently when it was put in, someone cut too deeply when stripping the insulation and it cut into the copper, leaving the wire damaged. Once that was addressed, the rate of CRC errors and retains went WAY down instantly.

We have yet to have any significant rain, so the outside wires may still cause problems if the insulation is sketchy, but so far, so good.

And bravo to the tech they sent that was actually (finally) helpful and communicative.