ios 18 photo shuffle stalls when selecting 'use album'

Given that the ios version of 'random' when using photos from my library to display on my lock screen / wallpaper is not very random and seems to repeat alot (it runs on 'featured' photos which im not sure how it decides these? (as I have not indicated which photos are 'featured') ) - i tried setting up a new folder named 'kids and family' and put 3 photos into it; as a test.

when creating a new photo shuffle for lock screen / home screen, I select

1. add new walpaper
2. photo shuffle *for type*
3. 'album' - instead of people, nature or cities
4. the frequency default is hourly

when choosing 'album' the default is favourites - which works instantly; but when i change this and point it to another folder (in this case, kids and family) it just stalls on 'use album' and continues to show the processing icon, but never finishes.

I can bypass this by selecing 'select photos manually' - and then I can select the 3 photos from the right album - but the whole idea of doing this was so I can add ALL the kids photos into this folder (searching by their name, selecting all and adding to the folder 'kids and family') - without having to select each photo individually.

is this feature supposed to work, or is there a bug in this that I have to use this work around?

• weird update / edit - so doing the above work around; you can only select up to 50 photos in this process. So i cancelled out and try re adding the entire folder (choosing kids and family instead of 'favourites' - and it worked straight away.. ) so something going wrong on the back end? or do I need to have a minium number of photos in this album for this to work correctly?