yep, I writted to the support coz have same problem, and they said that know about it...

when u do the subs'... the new player, is in the field, and one can not cancel the substitution... so if, who you substitute is injured, just after do the substitution... thats = you can not use the 2 players,,,, coz can not move the player that is in the field to another position or do something.... just is invisible.
bascally is something erroneous of the game, a fail.... that sometimmes happen.... :/