I've checked and removed/added back the permissions. Reloaded the plugin. I cannot open any player's inventory by pressing R when looking at them.
I unloaded then loaded the plugin. The errors at the bottom are me pressing R while looking at a player.

02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'BaseNetworkable.ShouldNetworkTo_Patch1' method. (BaseNetworkable_ShouldNetworkTo_Patch)
02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'BaseNetworkable.GetConnectionsWithin_Patch1' method. (BaseNetworkable_GetConnectionsWithin_Patch)
02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'BaseEntity.SignalBroadcast_Patch1' method. (BaseEntity_SignalBroadcast_Patch)
02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'EffectNetwork.Send_Patch1' method. (EffectNetwork_Send_Patch)
02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'Item.SetItemOwnership_Patch1' method. (Item_SetItemOwnership_phrase_Patch)
02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'Item.SetItemOwnership_Patch1' method. (Item_SetItemOwnership_string_Patch)
02/07 10:37:42 AM | [Vanish] Automatically Harmony patched 'BasePlayer.Teleport_Patch1' method. (BasePlayer_Teleport_Patch)
02/07 10:37:42 AM | [Vanish] Load Data
02/07 10:37:57 AM | NullReferenceException: Object reference not set to an instance of an object
02/07 10:37:58 AM | NullReferenceException: Object reference not set to an instance of an object​

It might be that one server... I have another server and it's working fine... The erroring server will reboot today and maybe that will fix it.

Working fine for me as well 

Server restarted and resolved the issue.