I'm unable to set the thumbnail size and position of images I have uploaded. Clicking and.or dragging within the image mostly has no effect, or (in a somewhat random way) makes the displayed thumbnail boundary "flip" from a tiny size to a larger size in one of several possible positions. The border sometimes displays what appears to be handles for dragging the edges or corners but they don't respond to any of my mouse actions.
Finally, when I click the "update" button, the selected border doesn't dictate the thumbnail actually generated.
I have tried in Chrome and Internet Explorer in Windows 10 with much the same results.