diff --git a/CHANGELOG.md b/CHANGELOG.md
index e92549c4d..5da066f17 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -38,6 +38,8 @@
 * Fixed a threading issue related to BlockStates and persistent data
 * Fixed an error when the server was shutting down
 * Fixed #2721
+* Fixed #2662
+* Fixed #2728
 * Fixed Infused Hopper picking up items with a max pickup delay
 
 ## Release Candidate 19 (11 Jan 2021)
diff --git a/pom.xml b/pom.xml
index cf2dacbce..d86cf5324 100644
--- a/pom.xml
+++ b/pom.xml
@@ -349,7 +349,7 @@
         <dependency>
             <groupId>com.github.TheBusyBiscuit</groupId>
             <artifactId>CS-CoreLib2</artifactId>
-            <version>0.29.2</version>
+            <version>0.29.3</version>
             <scope>compile</scope>
         </dependency>
         <dependency>
diff --git a/src/main/java/io/github/thebusybiscuit/slimefun4/core/networks/cargo/CargoUtils.java b/src/main/java/io/github/thebusybiscuit/slimefun4/core/networks/cargo/CargoUtils.java
index 7b73eafe8..c79ec0b6a 100644
--- a/src/main/java/io/github/thebusybiscuit/slimefun4/core/networks/cargo/CargoUtils.java
+++ b/src/main/java/io/github/thebusybiscuit/slimefun4/core/networks/cargo/CargoUtils.java
@@ -16,6 +16,7 @@ import org.bukkit.inventory.Inventory;
 import org.bukkit.inventory.InventoryHolder;
 import org.bukkit.inventory.ItemStack;
 
+import io.github.thebusybiscuit.cscorelib2.inventory.InvUtils;
 import io.github.thebusybiscuit.slimefun4.implementation.SlimefunPlugin;
 import io.github.thebusybiscuit.slimefun4.utils.SlimefunUtils;
 import io.github.thebusybiscuit.slimefun4.utils.itemstack.ItemStackWrapper;
@@ -310,7 +311,15 @@ final class CargoUtils {
     }
 
     @Nullable
-    private static ItemStack insertIntoVanillaInventory(ItemStack stack, Inventory inv) {
+    private static ItemStack insertIntoVanillaInventory(@Nonnull ItemStack stack, @Nonnull Inventory inv) {
+        /*
+         * If the Inventory does not accept this Item Type, bounce the item back.
+         * Example: Shulker boxes within shulker boxes (fixes #2662)
+         */
+        if (!InvUtils.isItemAllowed(stack.getType(), inv.getType())) {
+            return stack;
+        }
+
         ItemStack[] contents = inv.getContents();
         int[] range = getInputSlotRange(inv, stack);
         int minSlot = range[0];
diff --git a/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/items/magical/KnowledgeFlask.java b/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/items/magical/KnowledgeFlask.java
index 99744102d..1e1a5c3ab 100644
--- a/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/items/magical/KnowledgeFlask.java
+++ b/src/main/java/io/github/thebusybiscuit/slimefun4/implementation/items/magical/KnowledgeFlask.java
@@ -1,5 +1,7 @@
 package io.github.thebusybiscuit.slimefun4.implementation.items.magical;
 
+import javax.annotation.ParametersAreNonnullByDefault;
+
 import org.bukkit.Sound;
 import org.bukkit.entity.Player;
 import org.bukkit.inventory.ItemStack;
@@ -22,6 +24,7 @@ import me.mrCookieSlime.Slimefun.api.SlimefunItemStack;
  */
 public class KnowledgeFlask extends SimpleSlimefunItem<ItemUseHandler> {
 
+    @ParametersAreNonnullByDefault
     public KnowledgeFlask(Category category, SlimefunItemStack item, RecipeType recipeType, ItemStack[] recipe, ItemStack recipeOutput) {
         super(category, item, recipeType, recipe, recipeOutput);
     }
@@ -33,7 +36,13 @@ public class KnowledgeFlask extends SimpleSlimefunItem<ItemUseHandler> {
 
             if (p.getLevel() >= 1 && (!e.getClickedBlock().isPresent() || !(e.getClickedBlock().get().getType().isInteractable()))) {
                 p.setLevel(p.getLevel() - 1);
-                p.getInventory().addItem(SlimefunItems.FILLED_FLASK_OF_KNOWLEDGE.clone());
+
+                ItemStack item = SlimefunItems.FILLED_FLASK_OF_KNOWLEDGE.clone();
+
+                if (!p.getInventory().addItem(item).isEmpty()) {
+                    // The Item could not be added, let's drop it to the ground (fixes #2728)
+                    p.getWorld().dropItemNaturally(p.getLocation(), item);
+                }
 
                 p.playSound(p.getLocation(), Sound.ENTITY_EXPERIENCE_ORB_PICKUP, 1F, 0.5F);