Mac OS Sequoia not recognizing USB Flash Drives

Upgrading the maps of a Garmin navigation system that is connected by USB also does not work anymore.

15.1 update seems to have fixed the problem.

I haven't updated my iMac I am still on Sonoma 14.6.1 and I can't use my flash drives either.

for me it worked like this (sequoia 15.1)

after connecting the external HDD, i ran in the console the command

diskutil list

after waiting some minutes finally my partitions were listed and mounted.

Connecting the Garmin to a powered hub while the computer was turned off & then powering up didn't make a difference for me.

Yes, it's even weirder: it works exactly once (after the pram reset) and then after that it stops working.

The safe boot didn't work exactly like the normal boot.

I'm on a M2 pro

MacBook Air M2-Sequoia will not recognise any external device including Fujifilm X-T5 SD card but does

allow tethering.

All these devices continue to work normally on two retired MacBooks with older operating systems.

MJ wrote:

In my case, no the drives really aren't mounted.

I CAN manually mount them using Disk Utility, but that is a pain.

Are they encrypted? I have seen older versions macOS not automatically mount encrypted drives....not even offering to provide a prompt to unlock them. I believe I have even seen the same for un-encrypted USB drives before, but I am not 100% certain. I never had the time to look deeper the issue since were Macs in my organization & the user was not complaining about it....I only noticed it while working on the devices.

Are you connecting these drives directly to the USB-A ports on the Mac Studio but via some dongle in the MacBook? Maybe the difference between the two has to do with that dongle in the middle? Which dongle?

Would it work if connected directly, using a simple USB-A/USB-C adapter?

Open Disk Utility, see if the USB drive appears here even if it doesn't show up on the desktop or in Finder. Disk Utility can repair or reformat the drive with corrent file system, so the it can be recognized. Note: reformatting will wipe the files in the USB drive, operate with caution.

I have had this issue, in particular when I try to dump a .stl file for my Prusa Printer, which ONLY reads a Fat32 formatted USB. I will put a small, empty Fat32 USB drive in my M2 MacStudio running Sequoia 15.0 and if I try to copy anything from a 1k text file to a 50Meg .gcode file my Mac pukes and says there is no room on the drive. I have tried reformatting using Disk Utility to no avail. But..... I have succeeded and now use Path Finder from Cocoatech and that works perfectly. I have always used Path Finder off/on and I like it for some specific things. Now it is invaluable so I can work interchangeably with Fat32 USB drives. BTW, I saw this too on my old MBP which was the last Intel MB Apple made running both Ventura and Sonoma and they did not like Fat32 drive too. I don't know of an Apple solution to this issue. While one may exist, I can say that Path Finder works every time.

Same issue Late 2023 Macbook Pro 16 M3 Pro 18GB

15.0 (24A335)

Just called Apple about it, and they want to take it in for service

Weird behavior from any type of mass storage.

Initially I tried moving some files from my NAS to a known working SD Card formatted w/FAT32.

It hung, so I had to cancel it. Then I noticed I couldn't format it, stuck "Creating partition map", it wouldn't auto mount

So I tried various flash drives, some worked okay, then broke just a few minutes later.

Some USB drives wouldn't show up at all in Disk Utility, even when booting directly into recovery mode.

On the support call we ruled out faulty flash drives, and USB C adapters.

PVRP wrote:

I have a similar issue with M1 Air and Sequoia (after updating), my external SSD in a HUB is not mounting.

The fix is to activate the option in security, always ask to connect accessories. Not ideal, because now a I have to allow everything I plug.

Once it asks about the one device, you can set that back to something else. It should remember the devices you approved.

PVRP wrote:

The only way it works with this SSD is with the option I mention. If I change to anything else, it doesn't mount.

Recognizing and mounting are two different things. If it doesn't recognize it, it certainly won't mount.

I would reformat the drive.

Just to add to the confusion, running MacOS 15.1 on an M1 Mac Studio, after the last update, it won't mount SD cards from any of my Fuji cameras, but it will mount SD cards from my Leica. The same thing happens with my M1 Mac mini running the same MacOS. The cards are visible in Disk Utility, but they won't mount.