The difference between the White and Very-Light-Grey (#F1F1F1) backgrounds, that appear for read and unread notifications in the Echo flyout, is hard to see.
An editor at https://en.wikipedia.org/w/index.php?title=Wikipedia_talk:Notifications&oldid=638151935#Notification_didn.27t_work_for_.7B.7Bu.7D.7D says he "wouldn't have noticed it if you hadn't mentioned it to me".
Coupled with the way that Echo Alert Notifications all get marked as read when the flyout is opened, this is probably leading to some people missing notifications.
See T78363: Special:Notifications does not mirror the read/unread statuses from the echo flyout.
To fix this let us use the Base80 color that is #eaecf0 instead of #f1f1f1in mw.echo.ui.NotificationItemWidget.less and increase the @opacity-low variable to 0.6.
Repo - https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/Echo