The output from Audio Instruments may have clicks, pops, and crackles during a live performance.
This issue can be caused by brief spikes in processor load required by some instrument or effect plug-ins at high sample rates and/or low buffer sizes. These processor overloads will usually not show up in Logic's Audio Performance meter. Raise the audio driver buffer size or reduce the song sample rate to resolve the issue.
To raise the audio driver buffer size choose Logic Pro > Preferences > Audio > Drivers and set the next higher value for the "I/O Buffer Size" setting.