It's irritating that I can't expand (especially as often it's a vandalism + revert pair that I don't need to care about).
|mediawiki/extensions/Echo : master||Make edit-user-talk notifications expandable|
As a possible workaround would be to go Special:Notifications page where edit-user-talk bundle is expanded. It does not provide much help though, since edit-user-talk notifications do not provide much details:
Compare edit-user-talk to flowusertalk- ... notifications