Error messages that are printed in-game (i.e. specifying an invalid/not online player via /tell should tell the sender in red "That player could not be found," but nothing is printed in chat) via the vanilla server are somehow being swallowed by Spigot. On some version of Spigot 1.8.3 it does not do this, so it occurred sometime between then and up to 1.8.8

I wasn't aware that these messages were printed in-game, until I was testing things on a 1.8.3 server, which led me to investigate this.

I did a brief search for this issue beforehand, so I apologize if this has already been reported before.