ExFat External Drive missing files on macOS

Unfortunately I'm out of ideas since the things I mentioned here have been what I've seen cause similar issues with older versions of macOS and external drive.

Perhaps it is another bug with the new exFAT driver that Apple is using with Sonoma. You can provide Apple with product feedback here:

Feedback - macOS - Apple

Maybe you can open a support case with Apple and have it escalated to an engineer.

In case you are not aware, in macOS Sonoma Apple changed the exFAT and FAT driver from being a Kernel driver to a user space utility so parts of it would have been rewritten. Not surprising they introduced numerous bugs.

macOS Sonoma 14 Release Notes | Apple Developer Documentation

What system did you use to format the drive as exFAT?

Try booting the Mac into Safe Mode to see if that makes any difference.

TudorPM wrote:

When I mount the drive on macOS almost 1TB of data (video files, projects and so on) is "not there"... the same data in present when the hard-drive is connected to a Windows computer.

Just had an idea here. In the Finder use the toggle to display hidden files by using Shift + Command + Period/Dot. I just recalled a lot of people have been mentioning issues where Sonoma is marking files as hidden. To make sure you have the toggle for displaying hidden files on, view the home folder which at the very least should show a ghosted/gray "Library" & "Trash" folder. The home folder is the one with your user account name & house icon on the Finder's sidebar, or the "Home" item on the Finders' "Go" menu.

Also, are the missing items located in one specific folder or located in multiple locations? Is there anything special about these "missing" items? Perhaps all the same type of file, created/edited on the same day, used by a certain app different than used for other visible items?

Check out this discussion, it's seems they've changed the exFAT driver in Sonoma:

External HD slow to mount every time I bo… - Apple Community

Did you install onto the Mac any apps that came included with the drive?

If so, that is likely the issue.

The Mac doesn't need any of the junk apps that drive manufacturers ship with their product. They are not recommended by Apple to be installed, and they do often interfere with the Mac's ability to properly access some drives.

Consider uninstalling those apps and reevaluating the situation.

Update macOS to 14.3.1 to see if that makes any difference. I saw someone post on here the other day this update may have fixed some exFAT issues.

Make sure to disconnect all other external devices from the Mac in case one of them is causing a problem. A few years ago I saw reports where people with a Wacom tablet connected would cause issues with external drives where some folders would be missing. Also make sure to connect the drive directly to the Mac.

FYI, the "Available" storage space is not the same thing as Free storage space. It is unfortunate that Apple chose to use "Available" almost everywhere in macOS since it is so misleading. See my other post here where I explain the macOS storage terminology:

Exlpanation of macOS Storage Terminology -- hwtech - Apple Community

Plus, storage values can differ slightly between different operating systems depending how they are calculated. Is it just the storage space value differences which are concerning you into thinking you have missing files/folders, or are there actual items you cannot see on this drive when using your Mac?