Hey @gixginge.
I've seen this happen occasionally. Usually all you need to do is play a couple rounds of ranked, and the ranks in the lobby will sync back up. Unfortunately you might need to solo queue to get the ranks synced back up so that you're close enough in rank with your friends so you can queue together.
If you're not even able to queue up for ranked on your own, what are you seeing when you try? Is it giving you any error messages at all?
/Kent