https://github.com/tgstation/tgstation/pull/51679 - pickup_item missing

code/modules/mining/machine_stacking.dm

@@ -92,6 +92,8 @@
 	return ..()
 
 /obj/machinery/mineral/stacking_machine/HasProximity(atom/movable/AM)
+	if(QDELETED(AM))
+		return
 	if(istype(AM, /obj/item/stack/sheet) && AM.loc == get_step(src, input_dir))
 		process_sheet(AM)
 
@@ -104,6 +106,8 @@
 			return TRUE
 
 /obj/machinery/mineral/stacking_machine/proc/process_sheet(obj/item/stack/sheet/inp)
+	if(QDELETED(inp))
+		return
 	var/key = inp.merge_type
 	var/obj/item/stack/sheet/storage = stack_list[key]
 	if(!storage) //It's the first of this sheet added