J3.x: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
Users see a white screen when editing a module in the backend (see: https://github.com/joomla/joomla-cms/issues/12456).
Versions affected
General Information
This pertains only to Joomla! version(s): 3.6.3
What is the cause
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
Be sure to clear your browser's cache and your Joomla! cache.