Mine would not reset either … until I rode it for a tenth of a mile or so.
Had the same speed sensor issue and decided to check for corroded connections. At the rear wheel things looked fine, so did the other end at the connection in the bezel. I used DeOxIT on all the connections and haven’t had an issue for the last 200mi. Last owner put shrink tubing on the link inside the bezel, and they are just wires, there’s no reason for this ECU error other than at the connection at the bezel in my opinion. Anyway, DeOxIT works great on my old stereos so I figured it would do a good job of cleaning and conditioning the wire connections on the bike, good stuff, hope it helps.