Yesterday I spent my time by checking titles of friends and more, today I tested this new feature with save/load formations.
I saw that this switch also the players, not only formation-tactics.
So that's why we can't use it during a match.
If the half of our players are in the bench, it just can't work.
In the old version (TE2015) it was only the formation that changed, not the players.
That's much better as I can use my two squads, the weaker for League games and the stronger for KO games.