Watch not measuring stand hours

I'm a dance teacher. Today I was teaching nonstop from 10:00am until 5:00pm. My Apple Watch series 4 only recorded 6 hours, including the earlier stand time as I went to the studio. It showed me as only standing from 10-12 and then not standing for two hours, then standing for two more and then missing another hour. I don't get it as I was constantly moving. I've previously noticed differences between my watch stand hours and my wife, who teaches with me. This was the most obvious as my wife's watch shows 11 hours during the same day. Any ideas what might be causing the watch to misread like that? It's annoying to be short of the goal when in fact you met the stand goal for the day.