So far only USB with FAT32 format works, exFat and NTFS formats do not work in my PST with the latest FW.
Also, I tried my brand new Kinston 64g, at first it could not read, I plugged in the Kinston 32g and it worked right the way. Both USB contains the exact same DSD128 files. I later tired the 64g again it read 2 out of 3 files. The third try it was able to read all files. It appears the 64g USB makes the PST works a lot harder to find these files. So I may just stick with the 32g for now.