I have a cheap Ebay odometer, mph, time device. If anything with a magnetic field gets close it resets. I had the tach mounted on the other side the handlebar stem and the speedo reset.....phone too close and reset.
It's a temperamental little bugger. Any magnetic field even close to the wire going down on the fork.....reset.
I moved the tach on the bar behind the fuel tank and keep my phone away and it has been fine ever since.