Apple are due to release OS X 10.11 "El Capitan" later today. Whilst we are looking forward to the performance and workflow improvements that the new release is set to provide, we urge caution to anyone tempted to upgrade immediately.
The new OS includes an updated version of the AudioUnit validation tool, which Logic Pro uses to test third-party plug-ins for compatibility. High-profile developers Native Instruments and Arturia have noted that their plug-ins do NOT pass this updated validation; we are sure that other developers’ plug-ins will also be affected.
A fix for the problem is underway, but we suggest that it may be safest to avoid the updated OS for the time being - especially if your workflow is at all based around Kontakt!