Hi, after doing some reading it appears this is a typical problem the Garmin has from the approach watches to any of the other models that can keep a golf score. Basically as described in other threads after you finish a round and save it on your watch it will not sync to the phone and appear in Garmin golf no matter what you do (delete scorecards that might be corrupt pfft, re-sync, power both devices on/off) . It did it once and that was it nothing since.
I can not recommend Garmin watches to any other golfers based on this. There is nothing more annoying that losing your score. You are better off using a dedicated app on your phone like Golf Pad. Do no waste your time or you will end up being disappointed. Garmin please do proper UAT on your software its not up to par.