It sounds like your USB stick has gotten into a weird state, likely due to the router either not dismounting it cleanly or holding on to metadata that's now confusing macOS. When a drive refuses to eject and Disk Utility can’t unmount or run First Aid, it usually means there’s a lingering process or system-level lock on the volume.
I suggest trying the following:
First, let's check what’s using the USB stick via the following command in the Terminal:
- lsof | grep /Volumes/Untitled
This will list any processes currently accessing the drive. If you see any results, make note of the PID (Process ID) in the second column. You can then stop those processes by running:
(Replace `PID` with the actual number.)
Next, let's try unmounting the drive using this command in the Terminal:
- diskutil unmount /Volumes/Untitled
If that fails, try a more forceful command:
- diskutil unmountDisk force /dev/diskX
Replace `diskX` with your actual disk identifier. You can find it with:
As a last resort, if using the Disk Utility didn't help, erase the drive.
Once cleaned up, avoid plugging it back into the router until you can confirm the router properly supports ExFAT or try reformatting it as FAT32 (MS-DOS) or APFS (if used only with Apple gear). Some routers are picky about filesystem support—even if they claim ExFAT compatibility.
