Failed to call hook 'OnPlayerSpawn' on plugin 'Loadoutless v1.3.3' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Core.Libraries.Permission.UserHasPermission (System.String id, System.String perm) [0x0000a] in :0
  at Oxide.Plugins.Loadoutless.OnPlayerSpawn (BasePlayer player) [0x00000] in <7c4339cc4aa34bd29dc4dec5e2bd3975>:0
  at Oxide.Plugins.Loadoutless.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x002a2] in <7c4339cc4aa34bd29dc4dec5e2bd3975>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <98321e516fc1420ea57d4d2088213a59>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in :0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in :0

[Error] Failed to call hook 'OnPlayerSpawn' on plugin 'Loadoutless v1.3.4' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Core.Libraries.Permission.UserHasPermission (System.String id, System.String perm) [0x0000a] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0

  at Oxide.Plugins.Loadoutless.OnPlayerSpawn (BasePlayer player) [0x00000] in <74432d91700e4eefa13de488aae895f9>:0

  at Oxide.Plugins.Loadoutless.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x002a2] in <74432d91700e4eefa13de488aae895f9>:0

  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <3606d2af539c45e4b5c61658e6a8b307>:0

  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0

  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <c2afd8354b8b4f3ca451cf5a1aa111c3>:0

What permissions do you have applied that result in this? I am not able to reproduce this result

Please keep in mind I just recently took over as the maintainer for this plugin so I am playing catchup with it so to speak. 

Every time a player enters the server, that error appears on the console.

A couple months ago somebody asked me to fix this plugin. The way it was coded was so annoying to navigate that I just rewrote most of it in a few hours. I didn't implement all the planned features yet, but I was planning to put in a claim request for this plugin when finished.

The way I fixed this issue was to move the contents of OnPlayerSpawn into a NextTick call and then verify the player is alive before adding the loadout.

Patching is enabled xD

"Patching is enabled"?. What do you mean by that Kan?.

Merged post

Will you be able to solve it?.

"Patching is enabled" was directed at me, so that I could submit the patch to fix the issue. I have no plan on patching this plugin at this time, due to other priorities, and I can't afford the context switch at this time. However, you can reference the start of the new implementation below, where this issue is fixed.
https://github.com/WheteThunger/SpawnLoadouts/blob/master/SpawnLoadouts.cs

I ask that the above only be used as an implementation reference. Don't install it since it will likely have backwards incompatible changes made before the official release. The goal will be to eventually make it backwards compatible with previous versions of Loadoutless and also other loadout plugins.

Please delete the old setup (lang file, data folder, config) and download the latest 2.0.0 partial re-write edition it fixes all issues.

Please follow update instructions for 2.0.0 fixes all known issues.