I'm seeing this in my console. The GUI Shop seems to work, but I'm not sure why this is appearding:

Failed to call hook 'OnLeaveNPC' on plugin 'GUIShop v2.2.48' (NullReferenceException: )
at (wrapper managed-to-native) UnityEngine.Component.get_transform(UnityEngine.Component)
at BaseEntity.get_ServerPosition () [0x00000] in <7bf03a36126644fea8d8443fd8e3aae7>:0
at Oxide.Plugins.GUIShop.OnLeaveNPC (BasePlayer npc, BasePlayer player) [0x00018] in <16b0439c38514cb08521834f8fec45f9>:0
at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x01aa8] in <16b0439c38514cb08521834f8fec45f9>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <9882f28dc2204b4dba514a9ad18f5042>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <9882f28dc2204b4dba514a9ad18f5042>:0

This keeps happening... any chance it'll be fixed? Not sure if it's actually affecting the actual functionality.

Failed to call hook 'OnLeaveNPC' on plugin 'GUIShop v2.2.48' (NullReferenceException: )
at (wrapper managed-to-native) UnityEngine.Component.get_transform(UnityEngine.Component)
at BaseEntity.get_ServerPosition () [0x00000] in <9357151e9e52423d80616f588927d318>:0
at Oxide.Plugins.GUIShop.OnLeaveNPC (BasePlayer npc, BasePlayer player) [0x00018] in <53eb7e6b75c5439a9d35abcc5ccdba5f>:0
at Oxide.Plugins.GUIShop.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x01aa8] in <53eb7e6b75c5439a9d35abcc5ccdba5f>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <60c318df79ed41688ea59335e48d61ad>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <9882f28dc2204b4dba514a9ad18f5042>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <9882f28dc2204b4dba514a9ad18f5042>:0​

I'd like to report that I'm still encountering this same error, too.