The readings seemed inaccurate as if the watch was Stuck within a lower heart rate range

My venu3 appeared to be incorrect this morning. It continued to respond to what I was doing, as in going up and down, seemingly correlated to my running pace, but overall it stayed in a very low hr range that I do not believe was accurate. 
This continued for over two miles at a slow jog (so well over 20 min) and then it jumped up suddenly to a very high range when I began increasing elevation. Those readings then seemed correct because of the time already elapsed where I was feeling way more fatigued than the watch was indicating. I tried moving the watch on my wrist to be sure there was contact. I hadn’t done anything differently. This is the second time this has happened. It wasn’t too cold out but definitely cooler temps.