When 3v3 displays an error when trying to queue, the way to resolve it is the following (providing every single person in the team does it and in order, no skipping any):

1. Clear the game cache (cog icon in the top right > clear up system)

2. Flush the DNS cache (open 'command prompt' on the PC and type `ipconfig /flushdns` and hit enter)

3. Reboot the PC (to be extra sure, reboot the modem / router too)

Unfortunately this happens because the internet is never 100% stable and any micro-loss of connection can cause data to not sync properly. Flash is also an old software language and is known to sometimes just outright fail to properly switch/clean data.

Please ensure all members have done this process

If that fails, sometimes switching leader, teleporting to a different area, or waiting a few minutes helps.