Photos all black when moved between folders

When I move photos from one folder to another on my online account, they are showing up as a total black screen with a tiny question mark in the middle that has no attached link. However, I can access them as pics on mobile devices. But no thumbnail, only icons showing.
I also cannot access my account dashboard anymore, and technical support has been useless. I have an original My Cloud and just bought a My Passport. I use a Mac Air laptop OS 10.15.6.
I am not at all happy with these products.