Fourth Zone not showing up?

Good morning! Loving the beta so far, happy to see how it develops between now and Launch.

I noticed in the “What to expect” patch notes via Steam that it mentioned “four changing missions across four zones” for the first few days. During my 8 hours of playing so far, spread across three significant log-in sessions, I don’t think I’ve seen the fourth zone anywhere. After the first few hours, I was also looking through the currently locked difficulties in hopes of seeing the preview picture on mission select.

I currently have seen Chasm Terminus, The Torrent, and the sandy-palace zone. Do I misunderstand what the “Fourth Zone” is? With the absence of being able to pick our mission, I feel like “forcing” the RNG in a sense would be very nice for mission variety. Having not seen the fourth zone yet makes me feel like the RNG could be tweaked a bit to push mission diversity a bit.