Hi MEB
I am having the same issue with opening Nikon raw-files in Affinity Photo via the Edit with.. context option in Apple Photos. In my case the raw file from Apple Photos shows up in Affinity Photo as a tiff.
Another Apple Photos -> Affinity Photo scenario that I am having is this:
1. Image (raw-file) open in Apple Photos
2. Press EDIT in Apple Photos to edit in Affinity Photos (see attached image).
3. File opens in the Develop person but no image is shown, only the grey background.
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If I press Develop -> Affinity Photos crashes (see attached txt file for crash info)
The raw-files have been shot with a Nikon D300. I would be happy to provide a NEF-file for you guys if you need it. Let me know if there is anything I can do to help in pinpointing this issue further.
All the best
/Henrik
Affinity Photo - Crash.rtf