One of the special sponsor tasks is bugged?

[kyankyan123]

In previous seasons this worked no matter where the players were - they didn't have to be in starting lineup and even not in subs, having them in your team was enough for this task.

Now, if they have to be in starting lineup, I have a problem, as I have only one 18yo as a starter and other four 3* youngsters in the reserves

If your next opponent is weak, you could use them in starting line-up and, sub-out just after the match starts.
Or else, just let them play if your are winning.