We're investigating this issue now. Did your game start with this team?
EDIT: Thanks for the replies - we're pretty sure we've identified what happened on our end and are working on a fix.
EDIT 2: For players stuck in queue right now, you will probably not be able to play Clash today, though you should be able to tomorrow. For tonight, it looks like you will be locked out of other queues until all Clash matches are done tonight (roughly 3 hours after Lock-In ends). We're extremely sorry for the error and will follow up as the situation progresses.
EDIT 3: For the curious, this error happened because an error in a related service lost track of the unique identifiers we use for Clash Teams. This caused those Unique Identifiers to get reused, making them... not unique. That's why a lot of people are ending up on teams they were on in 2017, since it was grabbing the identifier used in the previous tournament.