Hi Folks,
I've noticed a similar issue to this when managing images in the back end too. My co-admin brought it to my attention and we have both seen it in Chrome and Firefox browsers. The selected image does get updated, but hitting the update button dows not close the window. It is, however, an intermittent issue.
The other issue is that selecting an image within an article (to update or delete) does not generate any kind of selection indicator - I think previously a border appeared around the image to indicate it had been selected.
JCE Pro 2.7.11 and Joomla 3.9.5 using the default admin template for the back-end.