Hello @nnn
Looking at your example and speaking with the match team this is by design.
If the 1st team game and youth game are taking place on the same day, than being available for selection for the 1st team will take precedence over playing in a youth game.
If the youth game is on a different day the players will play, you could also temporarily drop the players down to the U21 team but that will need to be done before the match day.
This is something we could potentially change but it might be a complicated change when factoring in game start time, player travel etc.