Greg,
So here is the problem. My iPhone has started storing photos in HEIC format - High Efficiency Image Coding/Format - which requires its own codec which Microsoft fails to supply; it appears to be part of/include the MPEG-H HVEC video codec for which Microsoft charges 99 cents plus tax.
I spent all day looking at what photos had not transferred to me PC since mid-October, and the first one that gave problems was a .heic Not only did the Photo app cheke on the file, but so did Explorer when I attempted to drag and drop it onto my PC. No nice error message, but an assortment of Catastrophic Hardware Failure messages! I deleted that one file after screen-shotting the image, and then could drag everything else over. I launched the Photo app, which showed blank boxes for the heics, but a link to MS to buy the missing codec. I installed it, and then the images are shown in Photo.
Does this stop the Photo app hanging during imports? No, or at least not yet. It appears that MS were totally unaware of this new format and what they need to include in their updates to handle it, At least now I can drag and drop all my new photos as I wait in hope that someone will fix this issue.
Please forward these details to anyone at MS you are in contact with.
Thank you