Client stays looking for a match that never starts

Normal draft or Solo/Duo ranked Find match shows "Match Found" bur never starts a match, It stays for very long supposedly waiting for all party members to accept. But after 1 minute (!) or so, it shows "a player didn't accept the invitation" and starts looking for a match again. After a while (15 min+ here) it just stops looking for a match.

You can start looking for a match again. Rinse, repeat.