Proguard obfuscates -keep public class files

I have a library project that uses Amazon mobile analytics. When I try to create a .aar artifact file, proguard gives me

:app:proguardRelease
Warning: com.amazonaws.auth.policy.conditions.S3ConditionFactory: can't find referenced class com.amazonaws.services.s3.model.CannedAccessControlList

Warning: com.amazonaws.util.json.JacksonFactory: can't find referenced class com.fasterxml.jackson.core.JsonFactory

Warning: com.amazonaws.util.json.JacksonFactory: can't find referenced class com.fasterxml.jackson.core.JsonToken

Warning: com.amazonaws.util.json.JacksonFactory$JacksonReader: can't find referenced class com.fasterxml.jackson.core.JsonParser

Warning: com.amazonaws.util.json.JacksonFactory$JacksonWriter: can't find referenced class com.fasterxml.jackson.core.JsonGenerator

Warning: there were 66 unresolved references to classes or interfaces.
         You may need to add missing library jars or update their versions.
         If your code works fine without the missing classes, you can suppress
         the warnings with '-dontwarn' options.
         (http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass)
:app:proguardRelease FAILED

      

        
        
        
      

    

It turns out that all these inapplicable classes contain enum in their body. I tried to exclude the whole package that contains these classes from proguard obfuscation, but still the classes are undefinable which seems to me: either the flags don't affect the behavior of the proguard, or I have to add some other flags. Below are the flags I have used.

-keepattributes *Annotation*    
-keepattributes InnerClasses

#-keep class com.fasterxml.jackson.core.JsonToken { *; }
#-keep class com.fasterxml.jackson.core.JsonParser { *; }
#-keep class com.fasterxml.jackson.core.JsonGenerator { *; }

      

        
        
        
      

    

Can anyone please tell me how to fix this problem?

EDIT:

I prevented proguard from obfuscating the following classes / packages, that's why it generates these warnings and ultimately an I / O exception in proguardRelease.

-keep public class com.amazonaws.** { *; }
-keep public class com.fasterxml.jackson.core.** { *; }

      

        
        
        
      

    

Regards