fix: client writing to netvar error

[LPLafontaineB]

Description (*)

From some investigation I found that there exists certain cases that lead to the OnNetworkSpawned method to be called on NetworkBehaviors a few frames after their Awake and Start happened. These cases are during the client synchronization process, when late joining, if there are multiple additive scenes to load and the NetworkObject that this NetworkBehavior is attached to is placed in-scene in one of those scenes, except the last one to be loaded. In those cases, OnNetworkSpawned is called on all in-scene placed objects only after all additive scenes are loaded, which leads to this delay for the NetworkObjects in the first scenes to load.

Related Pull Requests

Issue Number(s) (*)

Fixes issue(s): MTT-2921

Manual testing scenarios

I could not reproduce the specific issue this PR addresses, but I tested that these changes make it so the NetworkBehavior's Update or FixedUpdate are never called on clients in the cases mentioned in the description and that it works properly as before on the host.

Questions or comments

If this fix is approved, I think it should also be applied to our other NetworkBehaviors that should only execute on the server.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds are green)

[SamuelBellomo]

removing urgent label, let's fix this properly. This shouldn't block this release

[LPLafontaineB]

Put on hold waiting for PR #477

[LPLafontaineB]

removed OnHold label as PR #477 is postponed

[NoelStephensUnity]

Just an FYI:
PR-1785 cleans up how and when properties are set. You can now rely upon "IsSpawned" without having to have a local variable to keep track during OnNetworkSpawned.
So this should work fine now:

private void FixedUpdate()
{
    if (!IsSpawned)
    {
        return;
    }
    ...//Rest of the code
}