Typo in my previous post, not that it matters, but I should have said "'18 Limited" (instead of "'19 Limited"). In any case, I believe (hope?) this issue has finally been resolved.
Probably had the car in the shop for a total of 2 months since I've owned it for this specific issue. Finally took a Ford field tech's onsite visit to get the local service department on the right track.
I don't understand all the details, but it sounds like a module involved in reporting trouble had failed in addition to one of the parking sensors. Since the reporting module failed, there were no diagnostics thrown to indicate which sensor had failed. This is what led to a painfully long diagnostic and repair time.
Once the failed reporting module was replaced, it quickly became clear which parking sensor had failed and since that sensor was replaced the initial trouble has not returned. Interestingly, among the parts replaced was the entire piece containing the flip-down sunglasses holder, backseat/baby mirror, and lighting & sunroof control buttons - I guess the diagnostics component that had failed is housed in that module. Weird!
Anyway, in case it's ever helpful to anyone else who suffers this issue, I'm attaching the relevant parts of the service ticket here.
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