J3.x:Editing module shows module XML data not available
From Joomla! Documentation
Some modules installed in Joomla 3.4 and higher (that previously worked in Joomla 3.3.6) show an error when attempting to edit
Errors reported
"Module XML data not available" when going to edit module (with no fields appearing)
General Information
This pertains only to Joomla! version(s):- 3.4 and higher
What is the cause
Modules that have capital letters in their elements are now forced to lowercase during module installs (as a result of some standardisation in the installer). This results in case sensitive systems with the XML file being unable to be found.
How to fix
Ensure the module element e.g.
<filename module="mod_articles_category">mod_articles_category.php</filename>
has no capital letters in (as well as the appropriate XML file).