Strange 1 here, ever since getting my active 4months ago I've always had strava and Samsung activity tracker running at the same time (prefer strava for tracking my runs, samsung activity tracker for storing my runs/calories burnt etc). Moved to my watch 4 classic last week and both had still been fine together up until yesterday, had the Samsung activity tracker running in the background with strava open, finished my run closed strava and noticed the Samsung app only recorded 0.1km, thought was just a blip so went out today and noticed that now if strava is open it stops the Samsung tracker completely and if I then open the Samsung tracker it stops strava completely.
I tried out Strava for paddling today. I started Strava on my watch 4, and I noted that Galaxy Health was also started, so I shut it down manually. I thought I had done something wrong, but you suggest a deeper issue.