I have no idea what you mean by downloading a instrument pack from Analog Lab.
In my world you should not be able to hear Analog Lab sounds without using Analog Lab as a sound unit, if you playback recorded midi notes.
Are you using Analog Lab as a plugin you open inside Garageband? It sound like you open Analog Lab as a standalone application outside Garageband. Actually it sound like you use both, if you can close one Analog Lab application and then still hear sound.
As i wrote in my first post, then i assume you record midi notes. But are you actually recording audio?
Use Analog Lab as plugin inside Garageband, and don't open Analog Lab as standalone application outside Garageband. Then i assume you can have the GUI open inside Garageband without issues, as it's strange, if you can't. But as said, i don't know how Garageband work.
Your issue is'nt about Analog Lab. It's not about a setting in Analog Lab.
I assume you can ask about working with Garageband in a Garageband forum somewhere, if no one reply here in Arturias forums. I will guess your issue mainly is about using things correct.
Perhaps this topics i found by doing a quick search for Analog Lab and Garageband in my web browser can help:
https://forum.arturia.com/index.php?topic=108410.0https://forum.arturia.com/index.php?topic=106842.0