I have been dealing with this problem myself since the iOS 8 jailbreak has came out. For some reason phone calls will show up on the watch but any other notifications won’t. I have contacted tech support and they told me they did not have a fix for this at the moment.
But after working on it and trying a few things I found that enabling Airplane mode is a great way to get your notifications back. Now this has only been tested on my device. And hope it works for you.
What I did is bring up Control Center and enable Airplane mode. Now wait till your watch picks up that it has lost connection. Then turn off Airplane mode and wait for the watch to connect to the device. There has been a few times I have had to do this 2 or 3 times. But it would work after that.
To me this is way better then going to settings and forgetting the Bluetooth connection and then going to the watch and doing the same and repairing the devices. Let us know if this works for you.