How to perform add mutation when multiple different fields reference the same node. (Duplicate XID found)

Users Dgraph
1

I have the below as a snippet of my schema:

type Developer {
  id: String! @id
  name: String! @search(by: [exact])
  mergesAssigned: [MergeRequest] @hasInverse(field: assignees)
  mergesAuthorOf: [MergeRequest] @hasInverse(field: author)
}

type MergeRequest {
  id: String! @id
  title: String!
  assignees: [Developer] @hasInverse(field: mergesAssigned)
  author: Developer 
}

When doing a batch upsert mutation (seen below), I am unable to upsert 2 nodes if the mergesAssigned and mergesAuthorOf reference the same MergeRequest.

mutation { resp: addDeveloper(input: [ 
    { id: "gid://gitlab/User/3921" mergesAssigned: [ { id: "gid://gitlab/MergeRequest/346409" } ] mergesAuthorOf: [] name: "Bob's Ur Uncle" },
    { id: "gid://gitlab/User/9595" mergesAssigned: [] mergesAuthorOf: [ { id: "gid://gitlab/MergeRequest/346409" } ] name: "Johnny Tables" },
	], upsert: true) { entities: developer { id } }
}

Error given:
couldn't rewrite mutation addDeveloper because failed to rewrite mutation payload because duplicate XID found

However, the following mutation gives me no problems:

mutation { resp: addDeveloper(input: [ 
    { id: "gid://gitlab/User/3921" mergesAssigned: [ { id: "gid://gitlab/MergeRequest/346409" } ] mergesAuthorOf: [] name: "Bob's Ur Uncle" },
    { id: "gid://gitlab/User/9595" mergesAssigned: [ { id: "gid://gitlab/MergeRequest/346409" } ] mergesAuthorOf: [] name: "Johnny Tables" },
	], upsert: true) { entities: developer { id } }
}

Is this a DGraph problem or a data modelling problem? I feel more likely the latter - if this is the case, I’d be very thankful for any guidance.