Garage Band Instruments and Apple Loops 1.0 Issue

This is very uncomfortable as every time I need to update my other available updates I need to uninstall GarageBand so that that update does not show up in the App Store, then, once again, install GarageBand.

You should be able to install the updates to the other applications selectively.

When you see an update alert, you can click the alert itself, not one of the buttons below. This will open the updates tab of the AppStore and you can install each update you want to install.

Just ensure, that you have not set the System Preferences > AppStore to automatically install Application updates. I am using these System Preferences - only security updates will be installed automatically. This allows me to ignore application updates, until i am sure, that they will not cause unexpected problems with missing features.

This does not solve the problem with the broken update, however. It might be, that the update is simply not available for download right now.

Have you already tried, if the GarageBand update will install correctly, if you try it in Safe Mode?

If you start the Mac in safe mode, some caches will be cleared and third party system additions will be disabled and prevented from causing trouble. See: Use safe mode to isolate issues with your Mac - Apple Support