This is an issue many players on us forum already posted. I’ve too.
"The past couple of days, noticed this happening.
This started out while chatting in trade, when replying to someone, wanted to see who they were, what level, so forth. Typed /who joebob (made this name up, don’t worry) and I get a “0 players total”.
But then during one particular conversation I realized that several people couldn’t be seen. I started testing it out, and realized that I couldn’t even see half the people online in our guild when I did a /who guildname.
From talking to other people on the Arthas server, this isn’t just me. It’s not randomly different between different people either, the same people don’t show up on everyone’s /who list.
Anyone know what this is about, obviously either something is corrupted or there is an issue with the command not pulling correctly from the database? This isn’t an addon issue, our entire guild was talking about it last night and it was being discussed in trade chat also."
You will need to type /who character name-name of realm they are on. By typing /who character name will look for that person on your realm, and if they are on a different realm or faction, by doing so, it shows 0 players. Not sure if this is intended or a bug, yet this should solve your issue.
Pretty sure this came in BFA alpha with the new guilds & communities. It then got forced into game not working despite reports. Co joined realms and sharding make it worse.