See?
@BonusParadise yes it will work here at XenForo.
The likely culprit is a permission setting:
View attachment 86770
If this is set to 0, effectively no tag alerts will be sent.
It's worth noting that tagging doesn't work when editing a post. It will create the @ link but it won't alert the user.
If you're unsure exactly which usergroup the restrictive permission is set in, you can use Admin CP > Users > Analyze Permissions and input one of the names of the affected users (a user who tags someone and an alert is not generated) and that will tell you the value, and if you expand the info it will tell you exactly which user group the issue is in.