Topic on Extension talk:CategoryWatch

MediaWiki	1.31.1
PHP	7.1.8 (apache2handler)
Echo release 1.31
CategoryWatch	2.0, 2017-09-19 (542f9a1) 16:24, 17 April 2018
LocalSettings:
wfLoadExtension( 'Echo' );
#$wgRCWatchCategoryMembership=true;
wfLoadExtension( 'CategoryWatch' );
$wgCategoryWatchNotifyEditor = true;

When I move a page into or out of a category I get nothing.

This extension from the official repo has some bugs. A fix for your issue can be found here: https://github.com/gesinn-it-pub/mediawiki-extensions-CategoryWatch/commit/5094ed0b208c6704b9644af5f6dd9b6666ce2d54

Either patch the official repo or use https://github.com/gesinn-it-pub/mediawiki-extensions-CategoryWatch