Last night during my workout between 10-11:00 PM, I added 12 oz and reached 98 oz total, exceeding the 97 oz goal. I knew it was going to add some ounces to the goal after my workout. Ok fine.
I finished around 11:15 PM, noted my activity had saved successfully, and continued working on my floors.
At about 11:55 PM, I was working on my last 3 floors and added another 12 oz of water, totaling 110 oz with a 97 oz goal still showing. When I pressed the bottom button to exit back to the watch face, it immediately lowered my hydration total from 110 oz to 72 oz and increased the goal from 97 oz to 111 oz.
About a week ago I also completed 98 oz late at night then sat down to watch TV. While I was watching TV between 9-10:00 PM, I glanced at my watch and observed the hydration total drop quickly from 98 oz all the way down to 0 oz all by itself.
Note that I never, ever touch the hydration +/- buttons in the Connect app, to avoid any syncing problems. I only use the hydration widget on the watch.
I thought I'd seen all of the Hydration bugs, but these blow my mind.
