Yes, since the Odyssey release CQC suffers from matchmaking errors - very common, happen when matches end. They break the lobby, separate players who even after restarting the lobby can no longer match up and play together. It's a total disaster that breaks the whole Arena experience... So there may be 2, 3, 4 players still playing but whoever got matchmaking errors can no longer rejoin the running matches. And the saddest part is, FDevs are doing nothing to fix it (or at least players are unaware of any attempts to fix the problem).
On a more positive note, there are still quite a few CMDRs playing CQC regularly, regardless all the issues and they can be found on those two discord channels.