My heart rate graph gets stuck on a number intermittently. For example during an activity it will get stuck at a heart rate of 150 and continue to display this level and color, even as time moves forward, until the graph is just a straight box of color. This can usually be reset by turning off and on but does not improve with taking watch off and putting it back on. Is this something to be expected intermittently or should I pursue a new watch/return this one. The heart rate number itself changes while the graph is stuck.