For same unknown reason, Ruby rejected a number of friendlies requests in turn 11, season 17.
I checked with my friend in Belenenses and he said that i didn’t rejected any invitation.

Who invited who? Haven’t the invitations expired?

Nope, still got the emails. Wanna seen them?
Strangely all mentioned the same: Subject: Friendly Rejected 36 . But all were for different turns

3 friendly request for Belenenses, 1 for At Madrid and 1 for West Ham

Second possibility: they have accepted another team’s friendly invitation or another team has accpeted their friendly invitation for the same turn you proposed, in which case you’d receive a friendly rejected message. Could be it?