We have some report of El capitan users that our plugin are not validated by Logic X with the following message.
WARNING: 140: This application, or a library it uses, is using the deprecated Carbon Component Manager for hosting Audio Units. Support for this will be removed in a future release. Also, this makes the host incompatible with version 3 audio units. Please transition to the API's in AudioComponent.h.
I suppose Logic ensure a "treat warning as error"
We do not use Juce plugin framework though.
Still I am wondering if some people using the Juce plugin framework have the same issue under El Capitan.