Yesterday was my first ride, of any length, since getting back from a Seattle area trip (It was impossible to avoid having a Prius in your field of vision, and more electric bikes and cars than I have seen in my whole life.)
Before heading out, I pulled the velcroed elastic sleeve off the chainstay. It is one from Grin Tech, and covers the mass of connectors between the handlebars, controller, and motor. I unplugged and replugged the JST-SM hall plug. The silicone dielectric grease seems to be preventing corrosion. I rearranged the bundle of plugs hoping to reduce any strain on the wires.
To deal with the extra length of the hall cable, I had originally folded it directly back over the braided motor cable sheath. In retrospect, that tight 180 degree bend may have created a future failure. Anyway, 40 miles into my 70 mile ride, the problem occurred again, but only for a second or two, so I may have located the problem. Good thing too, as it was 99 F and humid.