This happens to me - it's not match plan for me as no subs are used up - a sub (always number 12) is randomly put into the first XI soon after the match starts with other players knocked out of position, so I have a GK up front, AML to AMC, AMC to AMR etc etc. I can make a sub to correct it, but if I'm not paying attention it can be really annoying.
I've tried deleting the game, reinstalling and starting a new save, but it's still happening.