Dashes in usernames can't be autofilled.
For example, when you start typing out a username with @, it starts suggesting usernames based on the letters you type. However, if I want to poke @Sam-Pinansky, it stops suggesting any usernames after the dash.
Technically, the username has a space in it, not a dash, it just comes out as a dash in the mention link. For people who have actual dashes in their usernames (e.g. "-----dog"), you can autofill using those dashes, but they are removed in the mention link. Kind of overall confusing and probably not working quite as intended :V
Yeah, I find it annoying too every time I want to mention someone. I'm used to other forums where it works much better, not exactly a fan of NodeBB implementation :(
Space obviously breaks the auto-complete, just tried underscore too as that was a likely candidate for software to use as a space stand in. No luck.
Also, how are there that many Sams on here other than the boss we want to tag? All these Sam something users I've never seen post