Currently there is a link to [[Special:ListGroupRights]] but no link to the log where the change might be explained. This would have been useful for me when FlaggedRevs was removed from MW.org
[1] https://www.mediawiki.org/wiki/Thread:User_talk:%5Edemon/User_group_changed/reply
Version: unspecified
Severity: normal
Rather than adding a link, it make make sense to link the log instead of Special:ListGroupRights. That special page isn't tailored to the specific user at all, it just lists all groups on the wiki. The log includes the reason and who did it, so may be the more useful information here.
The Special:Notifications page (not the flyout) has 3 links, including the performer's entire log (but not the specific entry).
https://www.mediawiki.org/wiki/Echo_%28Notifications%29/Message_audit#Echo ("notification-user-rights")
I'm generally in favor of having primary and secondary links in the flyout's notifications.
There are 4 other similar bugs, that should be properly merged (copying useful comments, not just closing them as duplicates) into 1:
(I have no time, today)