The class com.amazonaws.services.lambda.runtime.log4j2.LambdaAppender which attaches to log4j2 is removed from the JAR following reduction, it is non-fatal but produces the given output:
2018-07-25 22:13:28,997 main ERROR Error processing element Lambda ([Appenders: null]): CLASS_NOT_FOUND
2018-07-25 22:13:29,356 main ERROR Unable to locate appender "Lambda" for logger config "root"