Weird. I had the same problem right before I updated. Old appointments appeared on the watch, but nothing new appeared on the watch... Just on the iPhone. I think I noticed it Monday night? The calendar in question is an Office 365/Exchange calendar. I turned it off on the iPhone, restarted watch and iPhone, turned calendar back on, and still only appoints up until Friday or Saturday showed on the watch. Appointments added Sunday and Monday appeared on the iPhone. I tired enabling Bluetooth only, then wifi only. No difference. I figured I would worry about it the next day... Maybe try thr Un-pair and re-pair thing, but the next day everything had finally synced to the watch. After that new appointments synced normally.
I think I installed the latest iOS and watch OS updates on Thursday. So far so good.
Sean