The most likely cause for this issue could be:
Wrong channel configuration
The master channel fader is not at 0dB
The user data is stored in the following locations:
Windows:
macOS:
To move all data, copy these folders to the other computers.
If you open a plugin and you see this:
Make sure that this option is disabled in Garageband preferences:
The problem might be if the Elapsed histogram mode is selected, but audio playback is stopped.
The solution is to switch to continuous mode for measurements or to activate a host playback.