Swift:URLSessionDownload file says it exists but it doesn't?

Ok, I have succeeded in downloading various m4a files as well as removing them via URLSession. My problem is in the final "completion" function of the URLSessionDownloadDelegate requirement, I sometimes get the following printed to console even though I check in my download func( before downloading) whether the file exists in the directory or not. Very confused. Here is message:

File download succesfully
    “CFNetworkDownload_1wGgxs.tmp” couldn’t be moved to “Documents” because an item with the same name already exists.
    The task finished successfully

Here is download func where I CHECK EXPLICITLY whether file exists:

func goDownload()
    {
        if let audioUrl = downloadUrl { //set at beginning

            let documentsDirectoryURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
            let destinationUrl = documentsDirectoryURL.appendingPathComponent(audioUrl.lastPathComponent)
            print(destinationUrl)

            // to check if it exists before downloading it
            if FileManager.default.fileExists(atPath: destinationUrl.path) {
                print("********** The file already exists at path")

                // if the file doesn't exist
            } else {

                print("---------------> Starting Download")


                currentTask = session.downloadTask(with: audioUrl)
                currentTask.resume()
            }
        }
    }

Here is completion func:

func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {

        print("File download succesfully")
        let documentsDirectoryURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!

        // lets create your destination file url
        let destinationUrl = documentsDirectoryURL.appendingPathComponent((downloadUrl?.lastPathComponent)!)

        do {
            try FileManager.default.moveItem(at: location, to: destinationUrl)

            //success
            print("************** SUCCESS File moved to documents folder", downloadUrl)
            playModeStreaming = false

            self.pausePlay()
            AudioPlayerManager.shared.play(url: downloadUrl)

        } catch let error as NSError {
            print(error.localizedDescription)
        }


    }

I have even implemented a checking func that returns whether the file exists or not and after getting the above message, it returns false:

func checkIfExists(url: URL)->Bool
    {
        return FileManager.default.fileExists(atPath: url.path)
    }

What is causing this? How can I make sure it downloads so that it can play the m4a?

from Swift:URLSessionDownload file says it exists but it doesn't?