I hope this thread gets a little bit of attention...
Topic: F1 2019 don't let us invite friends to ranked lobbies anymore.
Why they probably done that:
To ensure, friends don't boost each other to ranks they don't deserve.
To ensure, friends with D rank don't get invited to S or A lobbies.
This leads to:
Many players stopped playing lobbies at all. The playerbase is obviously smaller than in F1 2018.
S-Lobbies are rare. To find lobbies at all