Image loaded using send_data are half broken when loading multiple images in iOS

For reasons I don’t want to get into here I need to resize images that are coming from users cell phones (and are stupid large) from blobs on the fly when loading them using this tag

image_tag thumbnail_document_path(document.id), alt: "#{document.document_title}", class: "document-thumbnail"

this calls the thumbnail controller action

  def thumbnail
    document = Document.find params[:id]
    image_meta = document.image_details.first
    image = Document.get_image_for_display image_meta
    send_data image, type: "image/jpg", disposition: "inline"
  end

Document.get_image_for_display pulls the blob from a database, checks the metadata we save separately to see if it’s a PDF that needs to be converted to an image or a huge image that needs resizing, and then does all that and asynchronously sends the blob. This works fine on everything except for iOS. on iOS safari and Chrome if you’re loading multiple images this way at the same time this happens. If anyone has an explanation or solution for this I’d love to hear it!

Edit: This app shares a server and database with a C++ desktop app and does not(and can not) have access to the locations on the server where these files are stored and there are hundreds of thousands of files across hundreds of client servers so storing a resized version next to the full size one is off the table due to physical storage limitations. The issue only appears to happen when trying to convert and load more than 3 large images and then only the first image stays broken, the others will fully load, although it takes a while for them to do it.

Source: Ios Questions