I've been having this issue for a while where the watch won't change the brightness based on the enviroment around it. Say in a pitch black room, it won't auto low or in direct sunlight it won't get any brighter. It always stays at 4 which is the brightness I picked. Auto low brightness is on. Weird thing is sometimes rebooting the watch makes the auto brightness work again, but it only last for a while and it eventually gets stuck. I don't know what it can be. Is it a faulty ambient light sensor? Please help.
I recommend resetting the watch. https://www.samsung.com/us/support/answer/ANS00084702
If the issue still occurs, it will need to be evaluated by a certified technician. Please send a private message with the full model code and serial number. http://bit.ly/2XERsky