I tried a variety of reply and thank actions, in this topic: https://www.mediawiki.org/w/index.php?title=Talk:Sandbox&workflow=rrkvm14ffnu3cmx4
I did not receive any Notifications (onwiki or email) for any of the replies, or mentions. I confirmed that all my userprefs ...oh!
---> The "Flow" item has vanished from https://www.mediawiki.org/wiki/Special:Preferences#mw-prefsection-echo (but is still visible at https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-echo )
(Bug was first described in this topic https://www.mediawiki.org/w/index.php?title=Talk:Flow&workflow=rrecqewz0xlbhe93 )