Hey there UCSman,
Thanks for reaching out to the Apple Support Communities. To get started, is this an iCloud Shared Photo Library that you're using? If so, check out the steps listed in the following resource that may be able to help: How to use iCloud Shared Photo Library - Apple Support
Get help with Shared Library
- If you use a device with an earlier version of iOS, iPadOS, macOS, tvOS, or iCloud for Windows, you can't see content moved to the Shared Library. You can see your Shared Library on iCloud.com, or see it on a device that meets the minimum system requirements for Shared Library.
- If the library creator runs out of iCloud storage, content can no longer be added to the Shared Library and changes such as edits, favorites, and metadata adjustments no longer sync. To get more storage and access to other premium features, learn how to upgrade to iCloud+.
If not, have you had a chance to go through all the steps listed in the 'Related Article', If Shared Albums aren't working - Apple Support?
If you have gone through the steps in the resources above, we'd recommend reaching out to Apple Support directly from this link here: Get Support - Apple
Take care!