Apple Watch has started to record exercise minutes when im not exercising

Had my Apple Watch a few years now and it’s only ever recorded my exercise minutes if I record an actual workout myself or if it picks up I’m actually doing some sort of exercise. However, over the past week it’s suddenly changed and recording far too many minutes each day when I’m not even exercising. If I get up from my desk and walk to another room it records every minute and has never done this previously. It’s saying I have done 2-3 hours exercise by the end of the day when I have only recorded 45 minutes in the gym then have sat at my desk the rest of the day. I have tried everything to try stop this and even rang Apple support who didn’t really know what to do either. Has anyone had this before?