Vanilla client and vanilla multiplayer server. My ping and all other players pings next to the bar when you hit alt key in windows is 0.
Additionally, on same server, with same client, both vanilla, I see question marks by server difficulty after hitting f3.
The numbers shown in the tab list aren't the ping of the players. They're the value of the scoreboard objective that is fisplayed in the list slot (
/scoreboard objectives setdisplay list OBJECTIVE).Question marks is MC-265425, WAI.