Fix 2 entity loading issues

src/main/java/net/minestom/server/entity/Player.java

@@ -546,24 +546,32 @@ public class Player extends LivingEntity implements CommandSender, Localizable,
         if (!firstSpawn) {
             // Player instance changed, clear current viewable collections
             previousChunks.forEach(chunk -> chunk.removeViewer(this));
+
+            //TODO: entity#removeViewer sends a packet for each removed entity
+            //Sending destroy entity packets is not necessary when the dimension changes
+            //and, potentially, this could also be rewritten to send only a single DestroyEntitiesPacket
+            //with the list of all destroyed entities
             this.viewableEntities.forEach(entity -> entity.removeViewer(this));
         }
 
-        super.setInstance(instance, spawnPosition);
-
         if (dimensionChange) {
             sendDimension(instance.getDimensionType());
         }
 
+        super.setInstance(instance, spawnPosition);
+
         if (updateChunks) {
             // Warning: loop to remove once `refreshVisibleChunks` manage it
-            previousChunks.forEach(chunk ->
-                    playerConnection.sendPacket(new UnloadChunkPacket(chunk.getChunkX(), chunk.getChunkZ())));
+            if(!dimensionChange) { //The client already forcefully unloads all chunks & entities when the dimension changes
+                previousChunks.forEach(chunk ->
+                        playerConnection.sendPacket(new UnloadChunkPacket(chunk.getChunkX(), chunk.getChunkZ())));
+            }
             refreshVisibleChunks();
         }
 
+        synchronizePosition(true); // So the player doesn't get stuck
+
         if (dimensionChange || firstSpawn) {
-            synchronizePosition(true); // So the player doesn't get stuck
             this.inventory.update();
         }
 

src/main/java/net/minestom/server/entity/fakeplayer/FakePlayer.java

@@ -134,6 +134,7 @@ public class FakePlayer extends Player implements NavigableEntity {
     protected boolean addViewer0(@NotNull Player player) {
         final boolean result = super.addViewer0(player);
         if (result) {
+            player.getPlayerConnection().sendPacket(getAddPlayerToList());
             handleTabList(player.getPlayerConnection());
         }
         return result;