Can't edit modules after update to 3.6.3
From Joomla! Documentation
In some cases the backend module edit doesn't work or shows a white screen after upgrading Joomla.
Errors reported[edit]
Users see a white screen when editing a module in the backend (see: https://github.com/joomla/joomla-cms/issues/12456).
Versions affected[edit]
General Information
This pertains only to Joomla! version(s): 3.6.3
What is the cause[edit]
Some javascript used for module editing was modified, however the browser being used is still using the old cached version of the javascript which no longer works.
How to fix[edit]
Be sure to clear your browser's cache and your Joomla! cache.