Outside of when an article is first made, I've found it impossible to add images to articles that were created after the update. This includes images that are already on the wiki and I've tried to add via "Search the Site". All I get is "An error occurred while uploading the image", and that's it. I have had no problem adding images to articles created before the update.
I'vee had these troubles in Windows 10 as well as Mac OS... I don't remember the version but I can find out. Also, using FireFox 59.0.3 and Google Chrome 66.0.3359.181.