Photoshop saves corrupt files

Many of the files I save these days open back up with horizontal stripes of corruption across one or more layers.   It's like a few rows of pixels that has become scrambled.  Sometimes chunks of a layer has been deleted completely. Like imagine using the square selection tool and deleting random squares across the image.

I work on fairly large files (up to 20 gb) and 30+ layers.  I save them as PSB files.  I work on an iMac Retina 5K 27" late 2015 with 64GB of RAM.   AMD Radeon R9 M390 2048 graphics card.  I'm in Photoshop CS6 and Using El Capitain. 

Could this be a RAM issue?

Could this be a graphics card issue?