My Android customers (of the CrewNerd app) have been reporting a variety of mysterious errors when uploading workouts to Strava. There were timeouts, sockets closing abruptly, and protocol errors all happening randomly. But there were no reports of problems from my iPhone users.
After much experimentation, it looks like the problems (which only started a couple of weeks ago) are related somehow to HTTP2. If I force my Android code to use HTTP1.1, there are no problems.
Bottom line - I think Strava introduced a regression recently in their HTTP2 support.