Issue with EntityLinks in Project Online API

[Windows Server]

Hello everyone,

I'm working with Project Online and trying to retrieve task data via the API. While reviewing the metadata, I noticed that PublishedTasks have a navigation property called EntityLinks, but I couldn't find clear documentation on its purpose or usage.

What I Tried

I attempted the following API requests:

 

Retrieve EntityLinks for a task:

GET https://{sitename}.sharepoint.com/sites/pwa/_api/ProjectServer/Projects(guid'{validProjectId}')/Tasks('{validTaskId}')/EntityLinks

Expand EntityLinks within tasks: 
GET https://{sitename}.sharepoint.com/sites/pwa/_api/ProjectServer/Projects(guid'{validProjectId}')/Tasks?$expand=EntityLinks

Observations

When the project has tasks, the request fails with:

{
    "odata.error": {
        "code": "42, Microsoft.ProjectServer.PJClientCallableException",
        "message": {
            "lang": "en-US",
            "value": "PJClientCallableException: GeneralUnhandledException\r\nGeneralUnhandledException\r\nException = System.NotImplementedException: The method or operation is not implemented.\r\n   at Microsoft.Office.Project.Server.BusinessLayer.EntityLinks.ThrowIfEntityLinksNotSupported()\r\n   at Microsoft.Office.Project.Server.BusinessLayer.EntityLinks.ReadEntityLinksForEntities(Guid[] entityUids)\r\n   at Microsoft.Office.Project.Server.Wcf.Implementation.CSOMImpl.<>c__DisplayClass35_0.<ReadEntityLinksForEntities>b__1()\r\n   at Microsoft.Office.Project.Server.BusinessObjectMethodInvocation.InvokeBusinessObjectMethod(String methodName, IEnumerable`1 actions)"
        }
    }
}

If the project has no tasks, the request returns an empty response without errors:

{
    "odata.metadata": "https://{sitename}.sharepoint.com/sites/pwa/_api/$metadata#SP.ApiData.PublishedTasks",
    "value": [
    ]
}

Other navigation properties (e.g., Predecessors) work fine with a similar request.

Questions

What are EntityLinks, and what do they refer to?
How can they be created via the UI in Project Online?
Is there a way to retrieve them successfully through the API?

I couldn't find references for this error or EntityLinks. Any insights would be greatly appreciated!

Thanks in advance!

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