what? at least 4 players in oppoentìs side? i've never seen this neither i could imagine.

The ball possession dropped before i got the red card for my back defender... but it's reasonable to think that probably the system anticipated itself and the red card caused the drop in the ball possession few minutes before it happened.
I can confirm i immediately made a change to to have the third player as defender - just as i probably replaced an attacker and i was playing with 2 DML (so in my side) i had only 3 players in opponents side and that's the reason why the ball possession didn't go up again! very interesting.

thanks for all your feedback guys!