Data structure optimizations as per review.

core/io/multiplayer_replicator.cpp

@@ -341,8 +341,10 @@ void MultiplayerReplicator::process_sync(int p_from, const uint8_t *p_packet, in
 	if (cfg.on_sync_receive.is_valid()) {
 		Array objs;
 		if (tracked_objects.has(id)) {
+			objs.resize(tracked_objects[id].size());
+			int idx = 0;
 			for (const ObjectID &obj_id : tracked_objects[id]) {
-				objs.push_back(ObjectDB::get_instance(obj_id));
+				objs[idx++] = ObjectDB::get_instance(obj_id);
 			}
 		}
 		PackedByteArray pba;
@@ -717,8 +719,10 @@ Error MultiplayerReplicator::sync_all(const ResourceUID::ID &p_scene_id, int p_p
 	if (cfg.on_sync_send.is_valid()) {
 		Array objs;
 		if (tracked_objects.has(p_scene_id)) {
+			objs.resize(tracked_objects[p_scene_id].size());
+			int idx = 0;
 			for (const ObjectID &obj_id : tracked_objects[p_scene_id]) {
-				objs.push_back(ObjectDB::get_instance(obj_id));
+				objs[idx++] = ObjectDB::get_instance(obj_id);
 			}
 		}
 		Variant args[3] = { p_scene_id, objs, p_peer };

core/io/multiplayer_replicator.h

@@ -32,6 +32,8 @@
 #define MULTIPLAYER_REPLICATOR_H
 
 #include "core/io/multiplayer_api.h"
+
+#include "core/templates/hash_map.h"
 #include "core/variant/typed_array.h"
 
 class MultiplayerReplicator : public Object {
@@ -70,7 +72,7 @@ private:
 	Vector<uint8_t> packet_cache;
 	Map<ResourceUID::ID, SceneConfig> replications;
 	Map<ObjectID, ResourceUID::ID> replicated_nodes;
-	Map<ResourceUID::ID, List<ObjectID>> tracked_objects;
+	HashMap<ResourceUID::ID, List<ObjectID>> tracked_objects;
 
 	// Encoding
 	Error _get_state(const List<StringName> &p_properties, const Object *p_obj, List<Variant> &r_variant);