TL;DR: If you had previous unpaired your watch by wiping the watch (reset from the watch), instead of "unpair" from the phone app; and then repaired it again, try actually unpairing from the phone app and then repairing again. I have a S0, and the watch started to lag for me in the middle of my time with it (about 6 months into the 1 year I have had it). Lag with everything, beginning with raise to wake, to opening and switching between apps, to loading things. Today, I wiped the watch by unpairing it through the Watch App on the phone (click on the watch, then click unpair). Even this process hung for me. After it finished, I was able to repair the watch, and noticed that everything was faster. From raise to wake, to loading, to switching between apps. Even transitions are smoother and do not lag like they did. I was wondering why everyone was so in love with OS3, because up until now, for me, it wasn't that great. But now I know. Anyways, hope it helps someone.