How Do Linked Albums Update?

I now have some linked albums in my Meural library. These link to my iCloud albums and also to shared iCloud albums I am a member of (shared to me by another iCloud user). If I add or delete a photo in one of my shared albums in iCloud Photos, or the person sharing their album to me makes a change, these are reflected in my Meural library. It's quite quick for my iCloud to reflect changes to shared albums to me (less than a minute), but the Meural app seems to take a couple of minutes to sync, so it's refresh rate is much lower than iCloud's, but it does sync. 

I have another issue with linking to iCloud shared albums that I have described in another post. If the photos are JPEG then it works. If Apple HEIF and after a version of iOS 15, then the linked album is empty and cannot be synced. It goes through the download process but never refreshes. What is odd is if I save a shared album photo that is HEIF to my Photo library, make no changes so it remains as HEIF, I can then manually add it to a Meural library, so the HEIF format is not an issue for manual uploads and only linked albums. All my own photos in iCloud are HEIF and upload fine, manually and to linked albums. It's just linked albums that are shared to me in iCloud and that have been created in HEIF from a particular date when iOS was a variant of version 15.