Thumbnails not showing in preview or in icons.

Have tried the solutions suggested:

• Option/general/show thumbnails.
• Windows/control panel/folders/deselect show icons,select thumbnails,select show preview handlers
• Windows/control panel/visual effects/select show thumbnails instead of icons

I have the 2016 edition and thumbnails initially worked but stopped after a month or so. I don't think I changed any settings. When I search old files from 2015 version they have thumbnails in preview and next to file names but when I open and re save to 2016 version I lose the thumbnails on both file names and preview. Other threads seem to have same problem but I cant find solution.