If a new file is imported into Photo by dragging over from a Mac, the file will not open. The filename is also changed to a string of random letters and digits. Whereas if the exact same file is imported from a local folder (e.g. "In My iPad"), all works normally.
The problem only occurs when new documents are to be opened. If a file is dragged into an existing opened document only as a new layer, the image will load successfully (even though the layer will still be renamed)
This affects .afphoto, .psd, .png and .jpeg files. I haven't tested others.
Specs:
MacBook Air M1 + macOS 12.3,
iPad Air (2019) + iPadOS 15.4
Affinity Design for iPad (1.10.21)
See the screenshot below – the left file was opened normally from Files, whereas the right file was dragged in.