Vigorous minutes

I have been using my Venu 2 plus for 18 months and it has worked flawlessly. Two weeks ago it suddenly started classifying all my activity minutes as vigorous even when my heart rate was in easy or moderate. I did a reset and that cleared the problem but unfortunately it has started doing the same thing again today. My wife has a Venu 2 S and her device started doing the same thing yesterday. 

Is this a known software bug in Venu 2 devices