I´ve had this issue with one of my apps for almost 1 month now. I´ve been able to publish updates for two of my iOS apps, but one is stuck in this exact state that you are experiencing. I´ve created support tickets for it, but no feedback or resolution so far. For the app that is stuck I´ve tried canceling the submission, adding new builds, changing the version number, updating metadata, etc, to no avail.

I have this exact issue at the moment. My app has been in this state (ready for review, and waiting for review) for about 2 weeks now. How did you get this sorted?