Not able to Relocate Sound Libraries back into Mac

The link is lost.

The next steps depends on the actual state of your setup. What is the exact content and folder structure on the external drive. Do you see a Library folder?

The approach can look like this:

• On the external drive: Rename the Library folder to a temporary name. Let say "TEMP".
• Let Logic download all the Essential Sounds.
• In Logic Use the Relocate Sound Library command to relocate the Library on the external drive. This create a new Library folder on the external drive.
• Quit Logic. Command-Q.
• On the external drive: Rename this new Library folder. Let say to "NEW".
• On the external drive: Rename the "TEMP" folder to "Library".
• Start Logic. How things look now?

Warning: The above procedure depends on what exactly is on the external drive.

There are other approaches but they require more knowledge.

WD

If Logic started to download the Essential Sounds, it means the link to the Library on the external drive is lost. Something happened after the use of the Relocate Sound Library command. The Library is now located on the local drive.

Regarding the macOS restore it is easier to just restore a backup of the Sound Library if you even need to.

WD

As someone mentioned, if you relocated the library but then restored the system, the link is obviously lost. Logic was reverted to before the library was relocated so expects it to be in its original location, which is not, so it tries to download again.

You can stop the download, or install just the essential sounds if not possible to stop and then simply copy each library folder back to overwrite the current minimal library. When started, Logic will detect that they are installed, it simply checks for the existence of sounds, there is not an installation file that needs to be there.

Alternatively, you can leave it where it is, or organise it in any way you want (as long as you keep the original file and folder names: "Apple Loops", "Alchemy Samples", "EXS24 Samples" etc), delete corresponding folders in the original location and put symbolic links (not aliases) instead. This is what I've done and I freed up a tone of space on the main drive, just the programs there, and the big libraries on external SSD/HDD. Logic will see them just fine and even install updates in the correct location on the external drive.

Hope this helps.