Failed to call hook 'OnLootEntity' on plugin 'SortButton v0.0.5' (KeyNotFoundException: The given key was not present in the dictionary.)
at System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) [0x0001e] in <437ba245d8404784b9fbab9b439ac908>:0
at Oxide.Plugins.SortButton.GetSortType (BasePlayer player) [0x00006] in <e1a570aba77345d2b389eabb3b2cba21>:0
at Oxide.Plugins.SortButton.CreateButtonUI (BasePlayer player, Oxide.Plugins.SortButton+PluginConfig button) [0x00000] in <e1a570aba77345d2b389eabb3b2cba21>:0
at Oxide.Plugins.SortButton.OnLootEntity (BasePlayer player, BaseEntity entity) [0x000f5] in <e1a570aba77345d2b389eabb3b2cba21>:0
at Oxide.Plugins.SortButton.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0030c] in <e1a570aba77345d2b389eabb3b2cba21>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <3e46d2a997e94a3cb08cf065508cd483>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <1fe782f4b27a43ae85d29ebb2d56c007>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <1fe782f4b27a43ae85d29ebb2d56c007>:0

Same here :

Failed to call hook 'OnLootEntity' on plugin 'SortButton v0.0.5' (KeyNotFoundException: The given key was not present in the dictionary.)
  at System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) [0x0001e] in <437ba245d8404784b9fbab9b439ac908>:0
  at Oxide.Plugins.SortButton.GetSortType (BasePlayer player) [0x00006] in <11794d576f3b4accad534c1bb4d9fe7b>:0
  at Oxide.Plugins.SortButton.CreateButtonUI (BasePlayer player, Oxide.Plugins.SortButton+PluginConfig button) [0x00000] in <11794d576f3b4accad534c1bb4d9fe7b>:0
  at Oxide.Plugins.SortButton.OnLootEntity (BasePlayer player, BaseEntity entity) [0x000f5] in <11794d576f3b4accad534c1bb4d9fe7b>:0
  at Oxide.Plugins.SortButton.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0030c] in <11794d576f3b4accad534c1bb4d9fe7b>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <1e2d7ad0801a4037ab6a24578c814b54>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <1fe782f4b27a43ae85d29ebb2d56c007>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <1fe782f4b27a43ae85d29ebb2d56c007>:

Looks like an deprecated method is being used.
Replace in SortButton.cs:

private void OnPlayerInit(BasePlayer player)​

to

private void OnPlayerConnected(BasePlayer player)​

It works for me.

This is fixed in the next version.