04/26 13:30:05 | Failed to call hook 'OnIngredientsCollect' on plugin 'ItemRetriever v0.6.0' (NullReferenceException: Object reference not set to an instance of an object)
at Oxide.Plugins.ItemRetriever.OnIngredientsCollect (ItemCrafter itemCrafter, ItemBlueprint blueprint, ItemCraftTask task, System.Int32 amount, BasePlayer player) [0x00106] in <6c16e76d54ab4047863f31af08ccc084>:0
at Oxide.Plugins.ItemRetriever.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0041f] in <6c16e76d54ab4047863f31af08ccc084>:0
at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <23ba99f131254889867c71f0bd137b1d>:0
at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <157a94ee66ab4a7991faecd1eb84be3b>:0
at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <157a94ee66ab4a7991faecd1eb84be3b>:0

Are you sure that the symptom you describe is related to that error? That error is happening in the OnIngredientsCollect hook which is only called when the player attempts to craft an item. Vending machines cannot be related. Furnaces, and transferring items to/from containers, are not affected by this plugin at all.

Looking at the code for OnIngredientsCollect in Item Retriever, the only way I see a NullReferenceException being thrown is if the hook was somehow called with invalid input, such as called by another plugin (instead of called by Oxide), or another plugin altered a craftable item's recipe in a very wrong way, or another plugin interacted with Item Retriever's hook to allow communication with Item Retriever but provided invalid input. All of these possibilities are extremely unlikely, but I could possibly make you a custom debug version of the plugin to ascertain which of these was true.