Issue with Ranked Solo: only getting primary role 21% of the time (4/19 games)

Asking for a friend (legitimately; he has no idea how to use boards/forums).

He's been trying really hard to climb but in his last 19 games he's only gotten his primary pick 4 times. His queues are popping instantly, too, so it's not even that matchmaking is giving up on his primary pick after a short wait. He's a silver player, so I would have thought the player population should be sufficient - it's not like he's a Challenger and there's only 6 other people playing at the moment.

Is there a known bug at the moment?