Move Goals

I have noticed after the last 2 ios updates for apple watch 4, if I manage to better my move goal after exercise, say by 20 or 80 calories and the system recognises that I have achieved my goal by issuing a ring etc. After I remove my watch to take a shower, when I put my watch back on, the move goal drops by anything from 20 to 100 calories and therefore 20 minutes later my watch is saying I have not achieved my move goal???

Has anyone experienced this phenomenon, as it is very frustrating to achieve a move goal then a few minutes later you are back trying to top up your move calories once again?