[11:58:22] > Loaded plugin Placeholder API v2.2.5 by misticos
[11:58:34] > Error while compiling DiscordPlayers: The type or namespace name 'Cache' does not exist in the namespace 'Oxide.Ext.Discord' (are you missing an assembly reference?) | Line: 8, Pos: 25

You need to install the latest Discord Extension and restart your server.