Music "disapear" from player when adding new songs with Synctunes

I am using
Synctune Pro to synchronised my music (music stored on micro SD card, that was working fine on FP1). When switching to FP2, the folder was not recognised (even when switching from the “old” synctune file to the new syntune file) and I had to retransfer everything. I already noticed some funny bugs with the playlist disappearing before.

Now, I realise that when I transfer new music, the previously transferred music disappear from
the music library (either in the standards “Music” app or in Poweramp pro.

Any advises ?

Many thanks in advance

Try changing the USB mode. The default mode is “Mount SD card”. This mode hides the SD to the phone when connected to a PC (the SD is used as an external hard disk). Do the following: When your phone is connected to your computer, swipe down the notification bar and of the left side you’ll find a notification to change USB options. Choose “MTP”. This will show your internal storage and your SD card on your computer.

Thanks for your quick answer.

I did what you suggested, restarted Music and Poweramp but no improvement. I uninstalled both apps, reboot my phone, reinstall them but sill nothing (except 8 notification ringtones in poweramp and
"outlook sent mail" in Music)

To avoid misunderstanding,I am using synctunes for a WiFi synchronisation and it was working fine the previous
time when I resynced everything over Wifi so I assume it is something related with the udpates of the playlist or something.

FYI, when I connect my phone, the music (15.7 Go) is stored in Ordinateur\FP2\Carte