[Zubersoft]

Are you using Sync Library->Sync to another device, or Sync Library->Sync to a cloud folder? If you change one song in your library, then sync again, are you saying that sometimes takes 4 hours? Or did that happen after you synchronized after doing something that could modify all of the files like restoring a library backup file? If you delete all files, then every file would have to be downloaded, so if you are synchronizing to the cloud and your download speeds aren't that high, it could certainly run for 4 hours. Doing a sync directly between devices should always be much faster than that though. Are you utilizing SD cards or only the internal storage of the devices? Did you change the storage location under Settings->Storage or are you using the default?

Mike