GroupSessionJournal loading attachments error

Hi all, I had previously posted this on the Media Technologies section but didn't receive any replies so thought I would try my luck here. Apologies if re-posting questions on the forum in a short-ish time span is against the rules, but would greatly appreciate some assistance with the following situation regarding GroupSessionJournal and loading attachments.

I'm currently working on a shareplay feature that allows users to pull 3d models from icloud and view it via volumes/immersive space on the vision pro. Was able to get the sharing working with multiple windows recently so now all that's left is to be able to sync/share the model in the SharePlay session.

As I understand it, we should generally use GroupSessionMessenger for commands and light data like model positioning/syncing properties. Whereas for bigger pieces of data (images/videos/models), we should send these through GroupSessionJournal which the group session manages and syncs it for all users in the call.

I have a button to get the current user's model data and add it to the journal via

/// modelData is type `Data`
try await journal.add(modelData)

I have also set up a task to observe/receive updates to the journal's attachments in when receiving a group session.

for await groupSession in MyModelActivity.sessions() {
    ...
    tasks.insert {
        Task {
            for await attachments in journal.attachments {
                for attachment in attachments {
                    do {
                        let modelData = try await attachment.load(Data.self) // throws error here - `notSupported`
                        let modelUrl = writeModelDataToTempDirectory(modelData: modelData)
                        self.modelUrlToLoadForGroupSession = modelUrl
                    } catch let error {
                        print("Error: \(error)")
                    }
                }
            }
        }
    }
}

Not quite sure why I'm running into an error being thrown when attempting to load the attachment data on the other devices, any thoughts? The documentation for add(_:) and load(_:) say that the attachment should conform to Transferable but Data.Type should already conform to Transferable