HEIC pix seem to be the most problematic but sometimes do work.
Is it just HEIC files that have an issue or are there other types of files? An issue with viewing an HEIC file will likely have a different cause/explanation than a problem viewing a TIFF or DNG
I've tried to manually change the extension to .jpg and this doesn't help either.
An HEIC file is not a JPEG; they are different file formats, and changing an extension does not convert a file from one format to another. However, whatever they used to create the HEIC files (whether it was their camera, or maybe they saved it out of Photoshop) can very likely also produce a JPEG just as easily as it can produce an HEIC. If they can produce a JPEG for you, then Photo Mechanic 6 will have no problem viewing that.
That said, I am guessing those HEIC files were from an iPhone 16, and Apple has apparently made a change to how this generation of iPhone creates its HEIC files, which required our developers to make an update to how Photo Mechanic reads these files. These changes are available in the new version of Photo Mechanic, but as Photo Mechanic 6 is now end of life, it will not be receiving the update to support these files. If you'd like to check that the new version supports the files that Photo Mechanic 6 is unable to display, I would recommend
beginning a free trial of the new version of Photo Mechanic to check. If you still have an issue with these files, then please let us know. If you start the trial and it does resolve the issue and you'd like to purchase, since you mentioned you are an educator, please reach out to our support team, as we do offer
educational discounts.