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I had the same problem with my series 3 (also couldn't change watch face). At the Apple store they had no idea what was wrong, so we restored the watch to factory settings (which does a backup to your iPhone first), then restored data from the backup. That fixed it and it has been working fine since. It seemed a little heavy handed, but it worked. See https://discussions.apple.com/thread/7050656 for steps.
 
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