Hello, I had something similar happen when I had HIGH megabyte Picture size... normally my 5100 had zero issues and I did some high ISO tests and the picture size increased by about 3 to 4 megabytes... Depending on the software viewed in, I would get similar weird results.
What software are you using??? How many megabytes are the files? I downloaded into Windows Photo Gallery and it happened... when viewed in Lightroom they were fine so obviously that software could not handle the larger file size??
Just throwing a dart... a place to start...
Pat in NH