Venu 3 heart rate inaccurate

Upgraded from Venu 2 to Venu 3 -  

Have low resting heart rate - In 30's and 40-'s - Heart rate sensor in Venue 2 was very accurate compared to medical grade PulseOx - Sensor in Venu 3 shows much higher heart rate - IE - 50"s compared to 30's on PulseOx - 

Is this a defect in the Venu 3 or do I have a bad sensor?

Thanks