Player names in an externally hosted server are sometimes appearing as three question marks, instead of as their respective names. This is not client side, as the same appears in the server console. Note that the names are still present and commands work with them, they just do not appear in chat properly.

This is a function of the "thief's hood" from environmental... It is an intended mechanic mostly meant for PvP servers, it also hides your nametag in world... Aside from that it stops enderman stare aggro and reduces mob aggro more the further you level it up(PvE perks they added for some PvE utility)