We have used the extension CategoryWatch for more than 8 year for our internal wiki in OPS (Ontario Public Service). Our users have used to receive email notification about membership changes in any watched category. After we upgraded our wiki to MediaWiki version 1.28.0. We have lost this widely used feature. We have been rquested by many our users to have the email notification back.
As far as I know the issue is the new MediaWiki has removed many deprecated functions, which are used by the CategoryWatch extension. It could be a simple fix by replacing those removed functions with alternative functions.
My intention here is to fix this extension and share with the community.