when i had my 256GB micro sd card formatted to FAT32 it would occasionally stop responding and dissapear (on both the pc and the ap80) when accessing it via the usb cable to the pc. only rebooting the ap80 would make it appear again on the ap80 and also pc (over usb cable)
this problem seems to be fixed by switching to exFAT
ACTUALLY it just did it again with exFAT. i was trying to copy about 30GB to the sd card over the usb cable and the sd card just disapeared. and the ap80 rebooted by itself.
so far its done this with two identical sd cards:
Patriot EP Series V30 A1 MICRO SDXC Card, 256GB
firmware 2.0
the only other card i tried was a 128GB ADATA brand card and i never had the issue on that
everything else works 100% perfect, playing music off the sd cards, or transfering files when plugging the sd cards directly into the pc