In the past our products used to run like clockwork in GarageBand, but in recent years Apple has made several changes that has made it really difficult for us. We finally had to stop supporting GarageBand completely because it took too much of our time.
Here is a list of all our officially supported DAWs/hosts:
https://www.xlnaudio.com/support/topics/what-are-the-system-requirements-for-xln-audio-products