The total amount of optional content for Logic Pro and MainStage is greater than 51 GB, which might cause issues with your internet connection.
If you have issues installing the additional content, make sure you have enough storage space on your Mac. Then, try installing the additional content packages individually using the Sound Library Manager.
To open the Sound Library Manager, choose Logic Pro X > Sound Library > Open Sound Library Manager, or MainStage > Sound Library > Open Sound Library Manager. In the Sound Library Manager, select the checkbox for each content package you want to download, and then click Install.