Thanks for the quick reply!
When I went to upload these files here, I got a message that the selected photo was too big. So before going further, I thought I'd see if that also made a difference to importing the files. I've now tried resizing the photo (from 2074KB to 476KB) and was able to successfully import it.
However, this wasn't a problem earlier in the year when I did the test project. I had images that were even larger and they imported fine then.
Happy to upload the photos and project log file here, but just thought I'd give you this update in case that changes what you need.