I'm having a problem with the Garmin HRM sensor I use with my Edge 520. On yesterday's ride, for example, it was working when I started, and then stopped after about 5 miles or so. The HR space on the screen was either blank, or had some unlikely number - like 72 bpm while out of the saddle climbing a 1/4 mile 6% gradient. This continued for the next 30 miles, and then it started working again, and continued to work for the remaining 25 miles of my ride. I had JUST replaced the battery the night before, since it had been doing this for some time - the dropouts during a long ride. This is the second sensor this happened to. I got this one a couple years ago when the previous one got similarly flaky. I could understand failing completely, or giving out mid-ride and not working the rest of the ride, but working for 5-10 miles, then NOT working for 20-30 miles and starting again and working for the remainder? That makes no sense to me.

I thought it might be location-related, like maybe I'm riding through an area with a lot of radio frequency interference, but a big chunk of my ride is going the opposite direction on roads I was on earlier, so not working in one direction but working in the other also doesn't make sense.

Anyone have similar experiences with Garmin HRM sensors? Any idea what causes it? Do other vendors HRM straps do the same thing? I can buy a new one, of course, but it will eventually do the same thing, I imagine.