I am having a similar issue. I am trying to create a playlist accessing songs from both internal and external memory, by creating a .pla file with Windows Explorer (see link)
When I disconnect the USB, everything is fine - it plays from both internal and external memory. But if I reconnect via USB and just look at the .pla file, all the references to the external memory songs are gone (the internal memory songs are still there). Actually, I can connect via USB and the playlist remains intact as long as I don’t navigate to it in Windows Explorer (i.e., I can connect to recharge).
The SanDisk support team suggest I reformat the Clip Zip, reload the 01.01.18 firmware and all my songs, but that sounds a bit drastic.
It just seems odd that just navigating to the .pla files corrupts them, no matter where I save them. I made several copies that I thought would be “backups”, but they all get zapped. And I was hoping I could save the .pla somewhere on the computer, but apparently that doesn’t work either.
(btw, I connect in MTP mode)
Any recommendations?