I updated a bunch of sites yesterday after the 3.6.3 release. When I went to add the login module the edit page was complete white with a drop down box. I was deeply concerned and thought maybe this Gantry template was the issue. It was not. I found this page.
I refreshed the browser window and everything was fine. Basically came down to Joomla worked on their caching component and you need to manually refresh the page.
Another install I upgraded simply refreshing the cache did not work. I was using Firefox. Firefox is making it tough to find the delete recent history. I had to close out of the administrative area all together. Open a new tab and then the modules were be having the way they should.
The articles are a different story. When I go into edit an article I get the following message.
I can still edit and save the article
I hope this helps someone else out there.