Rich Push with thumbnail image and long press image not working properly after iOS 14 update

We recently added rich push notifications to our app, which worked well on iOS 13. Our notifications have two attachments, the thumbnail and the image you see upon long pressing the notification. To facilitate this, we add these like so:

Code Block 
         var hasMainImage = false
        //The order of elements in the attachments array matters!
        if let validImage = mainImage, let fileURL = self.saveImageAttachment(image: validImage, forIdentifier: "attachment.png"),
          let mainAttachment = try? UNNotificationAttachment(identifier: "attachment",
                                    url: fileURL,
                                    options: [UNNotificationAttachmentOptionsThumbnailHiddenKey : true])
        {
          hasMainImage = true
          bestAttemptContent.attachments.append(mainAttachment)
        }
         
        if hasMainImage == true, let validImage = thumbnailImage, let fileURL = self.saveImageAttachment(image: validImage, forIdentifier: "thumbnail.png"),
          let thumbnailAttachment = try? UNNotificationAttachment(identifier: "thumbnail",
                                      url: fileURL,
                                      options: [UNNotificationAttachmentOptionsThumbnailHiddenKey : false])
        {
          bestAttemptContent.attachments.append(thumbnailAttachment)
        }
         
        contentHandler(bestAttemptContent)

After iOS 14, however, we are no longer able to see the image for long pressing the notification (aka main image). We can compare side by side with an iOS 13 device so we assume that the images are downloading properly. I didn't see anything for push notifications or notification service extensions get called out in the iOS 14 release notes.