So, always been using a chest strap for HR with my Garmin 1030 for cycling. It's a Wahoo strap. With my 245 I get erratic readings after about 30 minutes of running. So, it's not a lack of contact issue. Tried my wife's wahoo strap and the same issue.
I know what a HR of 160 or 170 is, and I see sometimes 170, when I know it's in the 150s. It stays 'stuck' on that exact number for a few minutes, with no variation and then drops down to 155 or so. Any suggestions?