Excepción fatal: java.lang.RuntimeException con Klaxon json Kotlin Library

Estoy usando klaxon con mi aplicación de Android (proguard habilitado) Este error viene con la última versión de Android 8.0. ¿Alguna idea que causa?

Fatal Exception: java.lang.RuntimeException Unexpected character at position 2: '< (60)' com.beust.klaxon.Parser.parse (Unknown Source:24) cc.cc.api.JsonParser$Companion.parse (Unknown Source:15) cc.cc.api.JsonParser$Companion$processResponse$1$2.onCompleted (Unknown Source:52) com.koushikdutta.async.future.SimpleFuture.getResultOrThrow (Unknown Source:10) com.koushikdutta.async.future.SimpleFuture.cancel (Unknown Source:22) com.koushikdutta.ion.IonRequestBuilder$EmitterTransform$1.onCompleted (Unknown Source:25) com.koushikdutta.async.future.SimpleFuture.getResultOrThrow (Unknown Source:10) com.koushikdutta.async.future.SimpleFuture.cancel (Unknown Source:22) com.koushikdutta.ion.IonRequestBuilder$1.run (Unknown Source:55) com.koushikdutta.async.AsyncServer$RunnableWrapper.run (Unknown Source:14) android.os.Handler.handleCallback (Handler.java:789) android.os.Handler.dispatchMessage (Handler.java:98) android.os.Looper.loop (Looper.java:164) android.app.ActivityThread.main (ActivityThread.java:6541) java.lang.reflect.Method.invoke (Method.java) com.android.internal.os.Zygote$MethodAndArgsCaller.run (Zygote.java:240) com.android.internal.os.ZygoteInit.main (ZygoteInit.java:767)