Image manager not opening

Hi
Ver. 2.3.0.2
Was creating a new site using opencart, all going well uploading products and was finalising homepage banners when I stopped being able to click to edit/change images.
When I click an image I see a 'no entry' cursor which disappears when the cursor is moved.
I have googled and confirmed permissions are 777 and 755, deleted recently added images, backed up the site and imported back in, deleted my browser (chrome) cache, tried using IE (you know it's bad at this point) and restarting my system but still get no response when I click to change an image, or to select an image when I setup I add a new banner/product.
This is across all images, products and banners.
Any advice appreciated - it does look to be a common bug but I haven't found any solutions that work for me

Check the TOTAL Amount of images in your image/..... Sections,
and also CLEAR ALL Cache Sections, as well as other Places, where something
may be adding files - eventually to masses, without you'll ever be aware of.
I recall to have been reading about such 'incidents' somewhere a while ago.
Good Luck
Ernie