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.
Users see a white screen when editing a module in the backend (see: https://github.com/joomla/joomla-cms/issues/12456).
This pertains only to Joomla! version(s): 3.6.3
What is the cause
We have changed some JS Code and your browser is still using the old version which no longer works.
How to fix
To be sure clear your Browsercache and your Joomla! cache.