I've also seen this problem for a long time, I don't know what mod could be interfering and producing this problem since it is not mentioned anywhere in the log.

(12:00:31) | [ganK] ganK.Sparrow ツ was killed by bradleyapc (entity)
(12:00:38) | [ganK] ganK.Sparrow ツ has spawned
(12:00:51) | Failed to call hook 'IOnPlayerCommand' on plugin 'RustCore v2.0.4788' (FormatException: Index (zero based) must be greater than or equal to zero and less than the size of the argument list.)
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000fb] in <cf88a28c7fb44d36890d85a78331cc9d>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <cf88a28c7fb44d36890d85a78331cc9d>:0
(12:01:01) | [ganK] ganK.Sparrow ツ has spawned
(12:01:04) | [Monos] xupa was killed by Zeno-Sama[76561198212962105]​

Merged post

In my case I have noticed that it occurs when someone is invited to the clan, either using their name or steamid ... I don't know if it is already a problem with the clan mod that I use or something internal.

Which Clans plugin are you using? It seems like the plugin is passing an error to the core, not actually the core erroring. There is no format handling done in IOnPlayerCommand from what I can tell.