diff --git a/paper-api/src/main/java/org/bukkit/plugin/SimpleServicesManager.java b/paper-api/src/main/java/org/bukkit/plugin/SimpleServicesManager.java
index f3dd8490230b..2c2c12ce77a1 100644
--- a/paper-api/src/main/java/org/bukkit/plugin/SimpleServicesManager.java
+++ b/paper-api/src/main/java/org/bukkit/plugin/SimpleServicesManager.java
@@ -94,7 +94,9 @@ public void unregisterAll(@NotNull Plugin plugin) {
                         it.remove();
                     }
                 }
-            } catch (NoSuchElementException e) {}
+            } catch (NoSuchElementException e) {
+                // Outer HashMap iterator can throw after inner list removals invalidate its state
+            }
         }
         for (ServiceUnregisterEvent event : unregisteredEvents) {
             Bukkit.getServer().getPluginManager().callEvent(event);
@@ -135,7 +137,8 @@ public void unregister(@NotNull Class<?> service, @NotNull Object provider) {
                                 unregisteredEvents.add(new ServiceUnregisterEvent(registered));
                             }
                         }
-                    } catch (NoSuchElementException e) { // Why does Java suck
+                    } catch (NoSuchElementException e) {
+                        // it2.remove() can corrupt the inner iterator's state on some list implementations
                     }
 
                     // Get rid of the empty list
@@ -143,7 +146,9 @@ public void unregister(@NotNull Class<?> service, @NotNull Object provider) {
                         it.remove();
                     }
                 }
-            } catch (NoSuchElementException e) {}
+            } catch (NoSuchElementException e) {
+                // Outer HashMap iterator can throw after inner list removals invalidate its state
+            }
         }
         for (ServiceUnregisterEvent event : unregisteredEvents) {
             Bukkit.getServer().getPluginManager().callEvent(event);
@@ -177,7 +182,8 @@ public void unregister(@NotNull Object provider) {
                                 unregisteredEvents.add(new ServiceUnregisterEvent(registered));
                             }
                         }
-                    } catch (NoSuchElementException e) { // Why does Java suck
+                    } catch (NoSuchElementException e) {
+                        // it2.remove() can corrupt the inner iterator's state on some list implementations
                     }
 
                     // Get rid of the empty list
@@ -185,7 +191,9 @@ public void unregister(@NotNull Object provider) {
                         it.remove();
                     }
                 }
-            } catch (NoSuchElementException e) {}
+            } catch (NoSuchElementException e) {
+                // Outer HashMap iterator can throw after inner list removals invalidate its state
+            }
         }
         for (ServiceUnregisterEvent event : unregisteredEvents) {
             Bukkit.getServer().getPluginManager().callEvent(event);
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryPlayer.java b/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryPlayer.java
index d8aae267a038..2417d8829237 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryPlayer.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/inventory/CraftInventoryPlayer.java
@@ -164,7 +164,12 @@ public int getHeldItemSlot() {
     public void setHeldItemSlot(int slot) {
         Preconditions.checkArgument(slot >= 0 && slot < Inventory.getSelectionSize(), "Slot (%s) is not between 0 and %s inclusive", slot, Inventory.getSelectionSize() - 1);
         this.getInventory().setSelectedSlot(slot);
-        ((CraftPlayer) this.getHolder()).getHandle().connection.send(new ClientboundSetHeldSlotPacket(slot));
+        // Paper start - Fix NPE when setHeldItemSlot is called on a disconnecting player
+        if (this.getHolder() == null) return;
+        ServerPlayer player = ((CraftPlayer) this.getHolder()).getHandle();
+        if (player.connection == null) return;
+        // Paper end - Fix NPE when setHeldItemSlot is called on a disconnecting player
+        player.connection.send(new ClientboundSetHeldSlotPacket(slot));
     }
 
     @Override