It seems like the various militaries need to do a better job of informing and enforcing social media policy, including auditing websites like Strava. You could also argue that Strava should be private by default, but I don't think you'd have much success persuading them of that.
Strava is the least of their problems. Despite all news articles in the last day I didn't come a cross a single previously unknown site mentioned in any of the stories. All those "experts" did, was showing known locations with a novelty overlay.
The heatmap is the graphic and interactive part that makes the story digestable, but there is no actual hard news in there. The story usually then shifts to being able to track users across bases, which is nothing exclusive to strava and mostly speculative when it comes to discovering actually secret deployments.
In the case of HMNB Clyde, that place also exists on instagram, which I find way more discerning, since by default geo-located pictures are even less obvious than a share my GPS-Track of my sports activities as default setting.
https://www.armytimes.com/news/your-army/2015/07/27/20000-so...
To reiterate: Strava isn't always on. These are activities people have actively chosen to log. The chance of it being someone out on patrol is... not high.
However, GPS is primarily a very high precision time signal, from which the current location is reconstructed. Basically, a properly designed software would do the proper time zone adjustment based on that, so the data should ideally be in local time everywhere without exception. Everything else would be a bug in my book.
Source: I've used lots of them and it's a real pain in the ass.