Strava Android fix
So I talked to Strava customer support. They suggested clearing the cache of the app on Android devices and updating to the latest version, as they recently pushed an update that should fix the issue. I tried it, and mine is working perfectly now.
I'm still going to double-check whether the data from my past 7 workouts, which were constantly showing syncing issues, has been saved correctly. But for now, this seems to be a working workaround, and I think the app is usable again.