USB Drive Size for music - for my Prius v (lowercase v wagon)

I have used 2 Flash Drives with 32gb capacity and 1 FD with 8gb capacity. Both work in my 2015 Prius v lowercase v for the Prius v wagon), but while all the albums and artists and songs are listed on the menu, only some of the albums and songs play. I created the FDs from original commercial CDs that I ripped on my Win7 computers and burned to the FDs on the same computers. The problem is that some albums play just fine and show the album cover. Other albums show nothing or some Egyptian Hiueorglyphics, but do not play the songs. All songs were stored in the .wma format since I used Windows Media Player to rip and burn the albums.

Any suggestions. I stored four albums on the 8gb FD thinking there was a capacity problem, but the same albums played and the ones that did not play from the 32gb FD did not play from the 8gb FD either. All songs and albums play fine on my computers.
I would expect that if there was a format problem, none of the songs would play or if the FD was corrupted, would not play anything either, but 30-40% of the songs do play fine, although have to advance to another album when have finished with one that plays.

Incidentally have tried the same FDs in my 2010 Camry Hybrid and again have the same problem except being older, takes much longer to load the master list of artists, etc.

Certainly is a pain, since I thought I could take a Flash Drive instead of 20-30 CDs when travelling, plus unlike my Camry, CD player only holds one disk at a time.

 

I am not certain that the size of the Flash Drive is the problem. I have read elsewhere that people with 16 and 32gb drives have no problems. I tried an 8gb drive with 4 albums (2 that worked on the larger fd and 2 that did not work) with no better results.
I could not find any 4gb flash drives.