Maybe it is recently installed plugin that is causing the problem them. Version 8.2.3 really was primarily an audit of the CSS and tweaking of some automated tasks for prefixing CSS and minifying CSS and JS file… nothing that would affect uploading an image.
There was a change with 8.1.6 (released in Jan) that would prevent selecting an image that was larger than what the server permits to be uploaded. If that is the reason, there should be a little popup error message. Maybe that popup isn’t displaying for you for some reason. Can you try selecting a small image to see if that makes a difference?