In some situations, Audio Unit plug-ins may not be automatically rescanned and validated by Logic Pro / Mainstage or Garage Band which are relying on the "AUvaltool" (Audio Units Validation Tool).
By following the steps below, you should be able to force a rescan for it to occur on the next opening of your prefered DAW :
- First, make sure to close Logic Pro / Mainstage or Garage Band
- In the Finder, choose Go > Go to Folder from the menu.
- Type ~/Library/Caches in the "Go to the folder" field.
- Press the "Go" button
- Make sure once inside this folder to delete the "com.apple.audiounits.cache" file.
- Make sure to also delete the "com.apple.audiounits.sandboxed.cache" file as well.
The next time you start Logic, the installed Audio Unit plug-ins will be rescanned and Logic should then startup normally.
In case any further problems would persists, make sure to also refer to the page below: