So, I have a 16-inch MacBookPro that just started showing this problem. Big Sur 11.2.3 installed.
The USB drives (yes, now two of them) will no longer auto mount. However, their locations are showing in the /Volumes directory as if they are still mounted - only not really since they are (a) not connected and (b) the folder permissions are locked.
What is more interesting is that on a 15-inch MacBookPro Big Sur 11.2.3 these same exact USB drives mount correctly (as they always had). Both machines are very similarly configured as to software. Very minimal system software installed (iStats and LittleSnitch) plus the assortment of developer tools, browsers, and editors.
Also, I can mount these drives via the terminal (bash shell) via "sudo diskutil mount -mountPoint /path /dev/disk2s1"
In fact, I can even mount them onto the /Volumnes/diskname mount point (/Volumes/Andromeda) and have them work until I unmount them.
Even in Disk Utility, I can see the volumes but not mount them - even if they were mounted and I unmount them with Disk Utility and then try to mount them again. Complete failure with: "Could not mount “Andromeda”. (com.apple.DiskManagement.disenter error 49180.)"
I have rebooted, rebooted in safe mode, rebooted and reset the SMC, etc. I have also tried to remove the /Volumes/Andromeda mount point while the drive was not connected. Nothing lets me, even when booting into the recovery mode. Always claiming it is not permitted.
This seems like some corruption within the OS and it is somewhere written to disk such that it does not clear up and has not cleared up over the days I have been trying to recover from this.
Solved ... for me at least ....Disk Utility -> First Aid
I had a very similar issue with my brand new Macbook Air M1 with BigSur 11.4
I have two Seagate 8TB drives, both formatted as eXFAT, which worked perfectly on my 2015 Macbook Pro Retina and an aged Dell M6800 running Windows 10.
No matter which drive, no matter how connected (Anker 6-in-1 PowerExpand usb-c hub. or another dongle usb-c to usb-3), I would ... a) not see the drive in Finder b) In Disk Utility the drive would be seen as not mounted, and would not mount manually c) powering up with the drive made no difference
Following an Apple Tip in this thread, I then ran First Aid on the drive using Disk Utility, but... FIRST: attempt a Disk Utility -> Mount, wait a while and close the error message that says can't mount .... important step. Then Run First Aid ...... a) select the show details tick box so you can see what's going on then proceed b) Accept any "can't mount" or "unmount" messages if they appear c) after very few minutes the drive was "repaired", mounted, visible in Finder, and all files & folders seemed intact. d) continued to work when drive disconnected & reconnected Most importantly, after the "repair" the drive still worked perfectly on my old Macbook & PC
I'll check out that the drive works with the other dongles and also do the same on my other 8TB drive.
I've just done that with the same results.
I agree 100%. What is wrong with this company? They freely make changes that affects our data and hardware and then ignore us, the customers, with all the problems their changes create. And it's not; like they don't have the money to support their customers.
Apple killed its desktop unit a few years ago. Alas. latest OS's show the loss.