Well ok, now finally after struggling with this issue with annotationProcessor can't be resolved, I can tell that it is a library issue or configuration issue on your side, since you are using 3rd party plugins.
In case of library issue, it might occur in case some of magic wasn't applied to generate javadoc tasks to include javadocDepts into classpath.
Issue with configuration might be that there are custom annotations, but no custom annotation processor, or you didn't include it in dependencies as annotationProcessor 'package.name:annotationProcessorModule:version'
Anyways, I had to remove custom annotations from my own library to be able to use artifact from jcenter, otherwise I would get
Failed to resolve annotationProcessor
all the time as well, when using my library in other project.
Here's the link to my question and my repository in case it might help you if you are developing those 3rd party plugin yourself:
Can't import AAR library with @IntDef annotations
https://github.com/vulko/AnimatedArcProgressView