Ideas
Aren't they? I got booted mid match after changing tactics/subbing. Same error. I and others get booted consistently on first game start - as tactics are evaluated and the game starts. This is being reported by multiple users, and not just with gauntlet mode. Go back over the last 12 months and see how frequently this has been reported for other live events.
Any error on the web call from the game to the server is reflected as a connection issue (generic error handler and message in the code). If EA exposed a decent or relevant error message, it would be possible to diagnose further, but they don't - we as a community then get stuck having to explain our connectivity (which CAN be a thing, but is NOT in these consistent and predictable occurrences) rather than EA jump in and investigate. It's a deflection.