Could not transfer photos from Library to External Hard Drive
I could not transfer imported photos on photos app to the external hard drive (Seagate Fast SSD). I've never had such a problem before until yesterday. My software is up to date. Usually, the photos will be shown as pictures (see attached pls) but yesterday, the transferred photos were seen as file pic. So, I clicked on one of them and the message say, " The file "IMG_1450.jpeg" could not be opened because it is empty. The photos previously transferred before yesterday are still there though. So, I tried transferring some photos from photo library to the desktop. Photos showed as normal.
FYI, I am low-tech. I would appreciate any assistance to help me fix this problem.
MacBook Air 13″, macOS 11.5