I actually came over here to look at feed back on the Fenix 5S because I have boxed up my Vivoactive 3 and printed a return slip before the 30 day return window expires. Very similar problems and hours spent with support trying to use the basic functionality. Perhaps that gives more info to process as I am sure they have a somewhat similar platform [I realize the differences]. It certainly makes me balk at "making the leap" into an even more expensive device.
I doesn't got the releation between your posting and this thread...
One of your activities (or courses) is corrupted (had the same problem). Found the solution in another forum (can't remember wich one...)