Today i encountered the issue again -_-
But for investigation purpose i might have an idea where the Dev's should look if they find any connection.
Loading Screen was normal for me, but afterwards you have the Option to Skip the Lineups, etc.
If you decide you want to do that normally in the left corner you see a "1/2" pop up and if your opponent does the same it turns into a "2/2", but for me everytime the bug occured it showed "1/12" and afterwards a bot took over my players.
The particular number and playstyle reminded me of the Bot you get in Pro Clubs.
There you have the option to play "ALL" or have the bot play the other players and you can tell the bot to Pass, Shoot, etc.
Because in FUT we dont have our own pro player we cant get passes.
Game maybe thinks it started a pro club game and took the players over.