I'm on Xcode 26.6, Tahoe 26.5.2 and a mini M4. However, the VP is 27 beta 2. It's working now. I'll keep rebooting if issues appear.

Ok, upon rebooting I find that there are two copies of the folder on device with exactly the same name. The previously invisible one was being accessed by the app. After deleting the copy, the app is accessing the files correctly. I don't know how two copies of the folder came to be or why one was invisible until reboot.