Dear Allison Peters,
When your drive crashed, and then was reconnected, your Mac created a second “mount point” for the external hard drive.
To over simplify things, the way that Mac’s work beneath the surface each external hard drive is considered a folder. When the drive came back online your computer considered it a new location rather than matching it up with the one that already existed. This was your computer’s mistake and not something that you could control.
Next, since that drives name–the /Volumes/Main Photo Drive-- mount point already existed the computer created a second one which it named /Volumes/Main Photo Drive 1.
On the surface all was well but unfortunately Adobe Photoshop Lightroom Classic uses very exact addressing for its data. To Adobe Photoshop Lightroom Classic Main Photo Drive 1 and Main Photo Drive are two separate addresses which is why the same drive is appearing twice in your Lightroom Folder’s Panel.
The best solution here is to shut everything down and power off your external hard drive. After you restart the computer, and without Lightroom running, use the OS Go To Folder Command to open up your /Volumes area.
If that second path, the Main Photo Drive 1, exists in the Volumes Folder then delete it. Once it’s gone restart the computer again and power your external hard drive back up.
If all went well it then it should now have its original name and path back. You can check this by using the Go To Folder /Volumes command again.
Assuming that the path is now correct, that there is no longer a 1 at the end of its address, you can restart Adobe Photoshop Lightroom Classic. At this point your Photos Go Here folder and all of it’s sub-folders should no longer be missing.
You might need to do a little additional cleanup to remove the false paths that Tony’s “find missing folder” command use created but that’s no big deal.
If everything works, and all is right again, then I urge you to take this opportunity to make a complete backup of that entire hard drive and your Adobe Photoshop Lightroom Classic Catalog. Sometimes these drive mount point errors are signs that a hard drive is going bad. Better to have a fresh backup then to be caught unprepared in case this ends up being more than a one-time inconvenience.
I hope this helps.