Sorry to hear you're having troubles as well. I don't think it's to do with the latest iOS as I have IOS10 on my phone. If you don't and you're having trouble that rules that out although being the first iteration of a new OS I had half thought that the slowness might be to do with that. Watch OS3 isn't available yet so it's not that. My pro subscription is still working but I've tried everything I can think of and still no joy.
Like you I've emailed support but nothing yet. Will post again when I hear anything.
UPDATE: I maybe wasn't clear before. The new version 5 IS working on my iPhone 5. I've also managed to get it working on my watch using the Classic app and it seems to be fine. The strange thing is both the classic version and Golfshot plus now look the same on the phone. However, Golfshot plus crashes on opening every time on the watch.
UPDATE 2 . Just received email from support. They confirm that there is a bug with Golfshot Plus and their suggested workaround is to install the ordinary Golfshot app and that should work On the watch. ( really just what I've said above). They say a fix is on the way.
FYI, I had the same issue with Golfshot Plus version 5.0 and they recommended downloading Golfshot version 3.0. Also, I found it confusing that they have two different apps that appear to have the exact same functionality. I confirmed with them that if you have a legacy lifetime membership or the Pro membership (I paid for it this year because the legacy lifetime doesn't have all the Apple Watch features) the Golfshot Plus and Golfshot apps function exactly the same. Frankly, the Golfshot app seems much more stable so I'll be sticking with that unless they do something in the future to differentiate the Plus from the regular app (I think they should just have 1 app with different subscriptions).