When you go for your walks, do you put the watch into 'Outdoor Walk' workout? If not, you should be. Without being in workout mode I believe the watch will only give you credit if your activity meets some heart rate requirement. I've struggled with this for years even when in the workout mode. I believe Apple's algorithm requires a heart rate reading, so if the watch isn't fitting quite right and failing to read your heart rate, that could do it. Many times when I'm trying to close my circles at the end of the day and I don't want to deal with what I'd call flawed logic, I just put the watch in 'Other' workout mode. Then you are supposed to get credit for a brisk walk and it seems to care less about the heart rate reading.