Unlimited Dining on Anthem - can't reserve all restaurants?

Just curious if this is something others have dealt with. We purchased the UDP for an Anthem cruise on October 4 (Vancouver-Honolulu), and most of the restaurants for lunch and dinner are available to pre-reserve in the app interface and the web interface, but strangely Wonderland is not available and Jamie's Italian is not available for dinner, only lunch. Both of those restaurants are readily available to book individually but obviously I don't want to book and pay for them in advance when I've already paid for unlimited premium dining. Also, Solarium Bistro is available to book via the UDP interface, but it's a no-charge venue, so not really relevant to the UDP. We've booked the UDP on another ship (the Wonder) and all venues were available to reserve on that ship, so this was confusing.

I thought that perhaps they're blocking people from pre-booking their most popular venues to save capacity for people paying for individual meals, but I had not gotten the impression that Wonderland was super popular. Perhaps I'm wrong about that, or maybe it's just so small on the Anthem that it books up fast?

I called RCCL about a month ago to see if this was a glitch or they're just blocking out some venues from pre-reserving with the package. The CSR told me that they could see that they weren't listed and said that was an error - they were all supposed to be bookable. She said she'd create an IT ticket to look into it. That was 4 weeks ago and it's still the same, so I called again to check, and this CSR verified what I was saying, put me on hold and asked her supervisor, then came back and said that some venues are just not available to book via the UDP on that ship, but they can be booked once we get on the ship.

Is this a known thing? Is it specific to the Anthem, or to Quantum-class, or just varies from ship to ship?