NRE in [SyncVar] NetworkIdentity when set for a newly instantiated GameObject

[OneFirefly]

Describe the bug
Instantiating a go, setting a [SyncVar] NetworkIdentity on one of its components, and then Using Server.Spawn(go); causes NullReferenceException

System.NullReferenceException: Object reference not set to an instance of an object
at Mirror.NetworkBehaviour.GetSyncVarNetworkIdentity (System.UInt32 netId, Mirror.NetworkIdentity& identityField) [0x00011] in C:\Unity\MirrorNG - SyncVar initialization bug\Assets\Mirror\Runtime\NetworkBehaviour.cs:397 
at TestComp.get_NetworkIdentity () <0x1756d80e490 + 0x00072> in <157148441a354f5e811588a77f5b3f35>:0 
at TestComp.set_NetworkIdentity (Mirror.NetworkIdentity value) [0x0000d] in <157148441a354f5e811588a77f5b3f35>:0 
at Test.TestSpawn () [0x0000d] in C:\Unity\MirrorNG - SyncVar initialization bug\Assets\Test.cs:33 

To Reproduce

• Create a server in Host mode
• Spawn a GameObject - use NetworkServer.Authenticated UnityEvent to call the spawn function:

//code in spawn function
var go = GameObject.Instantiate(prefab);
go.GetComponent<TestComp>().Identity = NetIdentity;
Server.Spawn(go);

• press Play and check Console for NRE

Desktop (please complete the following information):

• OS: Windows
• Build target: Unity Editor
• Unity version: 2019.4.10f1
• MirrorNG version: v49.2.1

Additional context
The problem is the same with a remote client instead of host mode

[github-actions]

🎉 This issue has been resolved in version 49.3.3 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀