Alterar para Spring-Boot 2.1.0.RELEASE a substituição de bean não é mais permitida por padrão. Isso causa o seguinte erro:

...
Caused by: org.springframework.beans.factory.support.BeanDefinitionOverrideException: Invalid bean definition with name 'org.springframework.context.config.internalBeanConfigurerAspect' defined in null: Cannot register bean definition [Root bean: class [org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect]; scope=; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=aspectOf; initMethodName=null; destroyMethodName=null] for bean 'org.springframework.context.config.internalBeanConfigurerAspect': There is already [Root bean: class [org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect]; scope=; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=aspectOf; initMethodName=null; destroyMethodName=null] bound.
at org.springframework.beans.factory.support.DefaultListableBeanFactory.registerBeanDefinition(DefaultListableBeanFactory.java:894)
at org.springframework.data.jpa.repository.config.JpaAuditingRegistrar.registerBeanConfigurerAspectIfNecessary(JpaAuditingRegistrar.java:135)
at org.springframework.data.jpa.repository.config.JpaAuditingRegistrar.registerBeanDefinitions(JpaAuditingRegistrar.java:88)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.lambda$loadBeanDefinitionsFromRegistrars$1(ConfigurationClassBeanDefinitionReader.java:364)
at java.util.LinkedHashMap.forEach(Unknown Source)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsFromRegistrars(ConfigurationClassBeanDefinitionReader.java:363)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitionsForConfigurationClass(ConfigurationClassBeanDefinitionReader.java:145)
at org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader.loadBeanDefinitions(ConfigurationClassBeanDefinitionReader.java:117)
at org.spr,ingframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions(ConfigurationClassPostProcessor.java:327)
at org.springframework.context.annotation.ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(ConfigurationClassPostProcessor.java:232)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors(PostProcessorRegistrationDelegate.java:275)
at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:95)
at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:691)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:528)
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775)
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
at org.springframework.boot.SpringApplication.run(SpringApplication.java:316)
at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:127)
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContextInternal(DefaultCacheAwareContextLoaderDelegate.java:99)
at org.springframework.test.context.cache.DefaultCacheAwareContextLoaderDelegate.loadContext(DefaultCacheAwareContextLoaderDelegate.java:117)
... 25 more

Com alguma depuração, achei queorg.springframework.data.jpa.repository.config.JpaAuditingRegistrar.registerBeanConfigurerAspectIfNecessary(BeanDefinitionRegistry) será chamado duas vezes. Seria bom se alguém pudesse explicar isso. De qualquer forma, a primeira instrução if nesse método deve reconhecer o bean do tipoAnnotationBeanConfigurerAspect já está registrado e faznã levar a uma OverrideException:

private void registerBeanConfigurerAspectIfNecessary(BeanDefinitionRegistry registry) {

    if (registry.containsBeanDefinition(BEAN_CONFIGURER_ASPECT_CLASS_NAME)) {
        return;
    }

registry.containsBeanDefinition verifica okey emregistry.definitionMap paraorg.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect. Mas oBeanDefinition se parece com isso

key = org.springframework.context.config.internalBeanConfigurerAspect
value = Bean of Type [org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect]

Parece quekey evalue estão misturados.