Hi,
If they popup while syncing and then disappear it usually means that some of your phone managers reorganize playlist files making MMA to think that they are removed. In your Case I gues sit is better to use WiFi then or Sync files with USB and then Resync playlists with WiFi.

i have a one plus x
i sync my playlist through usb and i can see them pop up for a second while the sync is still going then they disappear a second later and the sync finishes. no matter how many times i sync they still disappear
when i sync through wifi the playlists are added and they stay there