Why is my vivoactive gaining time?

I have had my vivoactive for 12 months and my husband has had his for 11 months. We both wear our watches everyday. We use them primarily for watch functions, steps, and to measure the distance and time of runs - but it regularly goes swimming, golfing, jet skiing, fishing - love it. I am an accountant and my husband is a builder and wears his on the building site everyday. I have not updated the software on the watches since we bought them ("if it is not broken don't fix it") but it has not skipped a beat. In the last 2 weeks, both of our watches have gained time - and not at the same time. My watch gained half hour and my husband's approx 15 minutes. Cannot locate anything in troubleshooting. Has anyone had this issue?