Update: This occurs when you attempt to add photos to an album from a shared album. To resolve this, you need to filter photos that originate from the shared album.

I was able to reproduce this issue in the Shortcuts app on my iPhone 14 Pro. You can replicate it by using two blocks: "Find Photos" with some filters and "Save to Album." This issue is more likely to occur when attempting to save a large number of media files to the album, typically around 5,000 to 7,000 items. However, it can also happen with a smaller quantity of items.