Your situation seems to be quite frustrating and has been going for some time now... argh.
On occasion I’ve also seen the “slow to populate” initial behaviour on the app screen, where all four main headings (Albums, Tracks, Radio, Playlists) are not present for some noticeable period of time. I don’t recall the last incident exactly, but it usually lasts a few seconds or gets resolved in the background while I select something to play.
That said, I have noticed that it is sometimes Albums but sometimes Radio which is missing. The protocol seems to be that the app asks the unit for a list of items, then displays it on the screen; delays in populating the list are likely caused by the app (iPad) to firmware (Uniti in my case) communication socket. For the Tidal favourite Albums, I guess they could be requested by the firmware in response to the app request... I don’t think they are necessarily stored locally, since new favourites selected elsewhere (eg in native Tidal app or via Roon) show up immediately next time you are in the Naim app (and vice versa of course).
Ages ago, I had bad comms and connectivity on a Qute: eithernet, wifi, didn’t matter. Obviously a totally different situation to yours, but a complete reinstall of the firmware and factory reset helped. Sure, you’ll lose your programmed favourite iRadio stations, any locally created playlists, and the custom names and settings for your inputs... but it might be worthwhile to give it a try as that is the best way to clear all internal caches and restore the unit to a completely known state. If your local collection (on your NAS or other upnp server) is large, you could try clearing the cache to flush memory.
Also, and I’m totally guessing here, is there any chance you’ve seen a slow down in app-to-unit connection? Do your rooms repopulate quickly if you pull down from the top of your screen to force the “find rooms now” function? Switching between wifi and Ethernet might show differences, just for test purposes?
In my experience, although other network functions can execute flawlessly, the Naim gear can be more prone to errors and odd behaviour that turn out to be connection related... even when that doesn’t really seem to make sense (and everything “just works” on other devices or native apps).
Not too helpful and no guarantees I know, but maybe a lift knowing other folks are wishing you well as you work through this one!