@andrewilley
In fact, I have neither updated the firmware, nor changed the version of PA. One day, I did the transfer via my mac with the Android transfer application and I renamed a folder on the fly. PA had probably started scanning (I think) and, seeing that the file was not taken into account, I did a complete rescan and it started to fail. The FIIO M7 does not have WIFI and is not connected to the internet, no update could have been done.
Yes, I tried and it works with the 256GB SDHC on folders containing MP3 albums independently. However, when in this configuration, I check all the folders, it does not work.
On the other hand, on the 64GB SDHC card, I put all the albums in a music folder, I scan music and it goes.