ProgressBar not updating in RecyclerView item row

I'm uploading some photos to my server, and want to view the progress of individual uploads. However, my RecyclerView isn't updating.

I know the progress is being updated, as I can see the progress in the my upload task, and the photo is uploaded to the server. I thought the viewholder would be what I would use to update the view, but my progress listener isn't' called.

Does anyone see what I have done wrong? Or could do better?

The PhotoUploadItem is the object that gets updated with the progress.

class PhotoUploadItem(var photoStore: PhotoStore) {

    interface PhotoUploadProgressListener {
        fun onProgressChanged(progress: Int)
    }

    private var uploadProgress = 0
    private var listener: PhotoUploadProgressListener? = null
  

    fun setUploadProgress(uploadProgress: Int) {
        this.uploadProgress = uploadProgress
        listener?.onProgressChanged(uploadProgress)
    }

    fun subscribe(listener: PhotoUploadProgressListener) {
        this.listener = listener
    }

    fun unsubscribe() {
        this.listener = null
    }

    fun progress() = uploadProgress
    fun identifier(): Int = photoStore.key
}

The PhotoUploadsAdapter takes a list of them.

class PhotoUploadsAdapter : RecyclerView.Adapter<PhotoUploadsAdapter.CustomViewHolder>() {

    inner class CustomViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)

    private val differCallback = object : DiffUtil.ItemCallback<PhotoUploadItem>() {
        override fun areItemsTheSame(oldItem: PhotoUploadItem, newItem: PhotoUploadItem) = oldItem.identifier() == newItem.identifier()

        override fun areContentsTheSame(oldItem: PhotoUploadItem, newItem: PhotoUploadItem) = oldItem.hashCode() == newItem.hashCode()
    }

    val differ = AsyncListDiffer(this, differCallback)

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): CustomViewHolder {
        return CustomViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.row_photo_upload, parent, false))
    }

    override fun getItemCount() = differ.currentList.size

    @SuppressLint("SetTextI18n")
    override fun onBindViewHolder(holder: CustomViewHolder, position: Int) {
        val item = differ.currentList[position]
        holder.itemView.apply {
            ///..... set other fields
            tvDisplayName?.text = item.photoStore.displayName
 
// THIS DOESN'T WORK
            item.subscribe(object : PhotoUploadItem.PhotoUploadProgressListener{
                override fun onProgressChanged(progress: Int) {
                    Log.i("UploadViewHolder", "${item.identifier()} has progress: $progress")
                    progressBar?.progress = progress
                    tvProgressAmount?.text = String.format(Locale.ROOT, "%d%%", progress)
                }
            })

        }
    }
}