Is "SceneReplicationInterface::on_sync_receive: Ignoring sync data" an error?

[isaaccp]

Tested versions

4.2 and HEAD @ aa5b6ed

System information

Windows 10

Issue description

I have two MultiplayerSpawner that spawn scenes ("Skeleton" and "Knife" respectively).

The multiplayer authority for all the spawners and spawned scenes is the server.

I call queue_free() in the server in order to remove spawned scenes.

Everything seems to work well gameplay-wise, but the debug log gets one of those:
"Ignoring sync data from non-authority or for missing node."
sometimes on the client from here:

godot/modules/multiplayer/scene_replication_interface.cpp

Line 879 in aa5b6ed

ERR_CONTINUE_MSG(true, "Ignoring sync data from non-authority or for missing node.");

I have added significant logging in the Godot source and I can see that when this happens:

• the notification for exit_tree is received by MultiplayerSynchronizer in the client, as a result
• _stop() is called on the MultiplayerSynchronizer in the client, which sets root_path_cache to ObjectID() (0).
• then ~1ms later the sync message arrives, root_path_cache.is_valid() is false as _stop() has set it to zero, as a result so sync.get_root_node() returns null and the message above is printed.

Here is a sample screenshot with my debug output:

I am not sure if I am doing something wrong or if it's just expected that somehow the "client" gets syncs shortly after being de-spawned and those cause this error.

If it's the latter, can we make this not appear in the debug log?

Steps to reproduce

Create a MultiplayerSpawner, spawn children including a MultiplayerSynchronizer from the server, remove them by calling queue_free() in the server

Minimal reproduction project (MRP)

I don't have a minimum reproduction project as of now. If the behavior described above is not expected, I can try to reproduce in a smaller form, but it may be hard given that it requires multiplayer.

[PatientLightning]

This is also happening to me, and I was wondering the same thing.

I have added significant logging in the Godot source

You're a champ, I was just starting to wish the error was more specific so I could determine if it was a real problem or not.

I think my understanding now is that the server is always sending sync packets from the node until it is de-spawned, then the client is receives the command to de-spawn before the the last sync packet is received and processed. Then when that last sync packet is processed, it throws an error because the node was de-spawned.

On one hand, It does seem reasonable that receiving sync data from a non-authority or a missing node is wrong, and therefore an error.
But in this case, we intended for the node to not exist, so seeing red in the log is alarming.

In the long term: I would suggest two things;
First, demote this error to a warning because I expect we will see it every time we de-spawn a node over the network.
Second, include more information like a node path and the peer id of the sender so we can comfortably ignore it or troubleshoot in case there really is a real problem, just like your modification does
Something like;
on_sync_receive: Ignoring sync data from non-authority or for missing node. Source peer id '1', NodePath '/root/level/ammobox'. This may happen if the node was recently freed

In the short term: I wrote a hacky little thing to avoid the error and keep my log clean

func q_free():
	$MultiplayerSynchronizer.queue_free()
	await get_tree().process_frame
	await get_tree().process_frame
	queue_free()

Basically, it frees the synchronizer then waits, then frees the scene. It's probably not foolproof, but at least it should help reduce red on localhost testing for now.

[Faless]

The fact that this case is reported as an error is indeed a bug, I've opened #87186 which should fix the issue.

[isaaccp]

@Faless it would be great if the error message could be updated to print something like what @PatientLightning suggested too, e.g.:
on_sync_receive: Ignoring sync data from non-authority or for missing node. Source peer id '1', NodePath '/root/level/ammobox'.

[Pshy0]

I am on v4.3.dev4.official [df78c06] and this is still happening.