Build error in 6.1, not in 6.0

[tough wolf]

How can this var tmp = new WeakObjectReference<GameObject>(authoring.prefab);
error into error CS1503: Argument 1: cannot convert from 'UnityEngine.GameObject' to 'Unity.Entities.Serialization.UntypedWeakReferenceId'?

It's calling:

#if UNITY_EDITOR
        public WeakObjectReference(TObject unityObject)
        {
            this.Id = UntypedWeakReferenceId.CreateFromObjectInstance(unityObject);
        }
#endif

Tested with an error 6000.1.6f1 and got a report from 6000.1.7f1
We use it successfully at work with 6000.1.4f1 and my personal project uses 6000.0.48f1.

Any idea why this is happening?

The authoring asmdef where this is used is guarded with:

"defineConstraints": [
        "UNITY_EDITOR"
    ],

[upbeat stone]

Just to check, your authoring doesn't have internal access to entities or another package does it

[tough wolf]

not directly. full asmdef:

{
  "name": "NZCore.Hybrid.Authoring",
  "rootNamespace": "",
  "references": [
    "Unity.Burst",
    "Unity.Collections",
    "Unity.Entities",
    "Unity.Entities.Hybrid",
    "Unity.Mathematics",
    "NZCore",
    "NZCore.Hybrid.Data",
    "Unity.Addressables"
  ],
  "includePlatforms": [],
  "excludePlatforms": [],
  "allowUnsafeCode": true,
  "overrideReferences": false,
  "precompiledReferences": [],
  "autoReferenced": true,
  "defineConstraints": [
    "UNITY_EDITOR"
  ],
  "versionDefines": [],
  "noEngineReferences": false
}

NZCore has internal access though