FAT32 USB pendrives show 0 capacity (M3Pro, Sonoma)

[pgolik]

Not sure if it's Apple Silicon or Sonoma issue, all I know is that it didn't happen with intel and Monterey, so posting here.
When I connect USB pendrives formatted as FAT32 to my new M3Pro MBP, either through an USB-A/C adapter, ort through a TB4 hub, I can read them without any problem, but I cannot write anything to them, as they show 0 capacity in Finder (see screenshots). I also can delete files, so it's not that they are read-only.
Interestingly, Disk Utility shows correct capacity and free space (screenshot with the same drive), but it doesn't help, still can't write.
It doesn't happen with the same type of USB pendrives formatted as ExFAT, so it's likely a software, not hardware issue. Also, the same pendrive that doesn't work in macOS is writable in a Win11 Fusion virtual machine, again pointing to software problems.

 

[bogdanw]

Have you tried Disk Aid or, better, checking the drive from Windows 11?

 

[pgolik]

Have you tried Disk Aid or, better, checking the drive from Windows 11?

It's not just one disk, I've had this problem with at least four different ones. And they work fine on the same machine when connected to a Win11 VM (in Fusion).

 

[bogdanw]

It's working as expected for me on Sonoma 14.1.2 Apple Silicon, USB 2.0 & 3 storage, cheap adapter.

 

[pgolik]

Resurrecting this old thread, as I finally found the culprit (with some help from a reddit post). It's a bug related to the DriveDx program. When I quit DriveDx, my FAT32 pendrives work as expected, with DriveDx running in the background, they show zero capacity. Weird, but that's what it is.