Not to bump a dead post. But just a slight update that I had this myself and just found this thread for the fix tonight!!! I had a fresh and clean install of 11.2-RELEASE, but the auto updates wanted me to "update" to 11.1 train. I have been holding off until either finding a fix, a workaround or the time to do another full clean install... However thanks to the FreeNAS Consortium Facebook Group, Jason Spradlin found this thread for me!!!
Yes, switching from to the old UI allowed me to properly select the 11.2 Train. I then clicked to search for updates and the update was there for the 11.2 train. I switched back to the new UI, and even though I also had to click to check for updates in the new UI as well, it did properly find the 11.2-U5 update for me! (Now just to wait until the kids stop watching Plex stuff so I can get it applied!!! lol)