I think, it's all about the engine, A.I.

I only struggle against teams, which are inactive. So this teams are played by the A.I.

At CL, I had the best opponent in my group (and for sure, we will play the final). He was a bit weaker (3%), I won away 1:6, opponent hadn't a chance to win this. Rematch, exactly same player on both side, my team full moraled/rested (like 1.game), we lost at home 1:2. We were also a lot better 7:2 SoT, we had the lead, suddenly opponent scored at 56' and 57'...
Only difference between those games: first match, manager was there, second match he wasn't there.

Same thing at league: we beat 2. place 7:0 -> this team conceeded 7 games no goal... manager was there. Today, we played vs last place (made 0 points, inactive), that team was ~80% weaker and we only won 5:0...

Nothing more to say.