I spent 25 years programming IBM mainframes - retired more than 20 years ago.  All I can say is - welcome to the wonderful world of computers.  

I owned an Apple II many years ago and learned that while Apple might produce some good machines, they are lacking in many ways in the world of support.  Also there are still those out there who think that a MAC can't be infected by a virus - which simply isn't true.   My suggestion is to buy a trusted MAC anti virus and start running it on your internal drive as well as you USB drives.  If you think you have or had a virus on a USB drive it is now on your computer - guaranteed.  Symantec is a good antivirus for a PC and they have them for MAC.  Then start first with the MAC itself with a virus scan before you go to a USB drive.

All that said - there are no programs in the world, MAC or PC or IBM mainframe that are bug free.  You could also have bugs or just plain idiosyncrasies that are hiding your photos.  Go to PhotoShop support and ask questions.

Debug, debug, debug.  That's what computers are all about.