Logic is installing sound libraries on the internal disc even after library has been relocated

„but they are going to the internal drive instead of the SSD. How do I fix this?“

you can’t. This is how it works unfortunately. Logic’s sample library management is a pain …

I noticed this problem too. If you do relocate via logic sound library manager, or manually via symbolic links (that's what logic does anyway), when you download new sounds the symlink is replaced by a new folder in the internal disk. You may get a "relink" dialog next time you restart logic, but it wont have the newly downloaded files.

I don't know if this is a bug, or a "feature", but given the inconvenience and annoyance, i'd call it a bug.

As a workaround i see the following options for now:

1. Download everything on the internal disk, then relocate. (you may need to use option 2 for futures updates and new content released)
2. Relocate once; then for each time you download new content via the manager:
   1. manually merge the files from the internal disk to the external disk (Finder does a good job merging, although it must be on directory at a time it seems).
   2. fix the symbolic link in /Library/Application Support/{Logic or GarageBand} -> /Volumes/ExternalDrive/Library/Application Support/{Logic or GarageBand} and similar for /Library/Audio/Apple Loops -> /Volumes/ExternalDrive/Apple Loops (or whatever you want)

There may be other options with bind mounts instead of symbolic links, but I'll have investigate that further, as there may be some drawbacks from that approach. Another temporary fix is to automate the option 2 above via some scripts either bash or via Automator. I'll give it a try and post a solution if folks would like.