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.

https://forum.joomla.org/viewtopic.php?f=709&p=3435967

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.

joomla_3_6_3_update_error

I can still edit and save the article

I hope this helps someone else out there.