I am using the latest version (1.7.2.471) on Windows 10. I can reproduce the problem by trying to open the files in question again. Affinity Photo crashes/closes right after loading.
I can provide the files. They're located inside the folder TGA Textures/Head/TGA/ after unzipping TGA+Textures.zip.
The files in question are Colour_16k.tga and Spec_16k.tga. The other files open just fine. Common characteristics between the files non of the other files have: both are 16k and are 700+MB in size.
The ZIP file can be downloaded from here (blog post): https://www.3dscanstore.com/blog/Free-3D-Head-Model
Alternatively, here are direct links - if you don't want to register. After registering it'll lead you to this page eventually which has the direct links: https://www.3dscanstore.com/blog/Download-Model
Thank you