Thanks, I upgraded to 2.5x and the problem seems a little clearer now. After the upgrade and using the M3U8 format, a couple of my playlists copied over fine (although I had to restore them in PlayerPro to fill them out with tracks), but the rest were all empty, and a manual restore (from the settings) doesn't do anything. I tried using both Google Music and PoweAmp to see if PlayerPro was my problem, but both of them recognize only the same playlists that PlayerPro does. I'm guessing this means the issue is on MB's syncing side.
If I try using the PLA format again, the two playlists that copied fine before the upgrade copied over again. The other playlists all failed: either "One or more of the parameters are illegal (Exception from HRESULT: 0x8007203F)", or "Error HRESULT E_FAIL has been returned from a call to a COM component", or "Data supplied is of wrong type (Exception from HRESULT : 0x8007065D)".
I also tried dragging and dropping the playlists one by one, but that produced the same results as before.
Thanks again for your help. Any further ideas?