There is ongoing issue (Bug) with mentioning @SomeUserNames_000000 (no matter if the user name is entered manually or his UserName is populated from Replied post).
Example:
Since the orginal mentioned Useruser has underscore in his name and when I replied to his post the below happen:
@Jeremy Launder_1715955576 some other user like Jeremy Launder is mentioned instead of
"Jeremy Moll"
Note: userName_withUnderscoreAndNumber needs to have access to the Space to replicate this issue
BTW: sorry guys for using your UserNames 🙄
You might also noticed some strange formatting hack above: when I wrote the user name in "@+usernameHere" then user name is becoming a link to his profile