Slice/Page method return Reference in R2DBC is invalid?

Question

In a nutShell , when i try to use slice/page as method reuturn value in r2dbc , i encounter the error , below is two difference api reference and corrsponding error stack

1. Flux<Slice<Object>>

Flux<Slice<ChatMsg>> findBySessionId(Long sessionId , Pageable pageable);

Caused by: java.lang.ClassCastException: class com.ifx.account.entity.ChatMsg cannot be
 cast to class org.springframework.data.domain.Slice (com.ifx.account.entity.ChatMsg and
 org.springframework.data.domain.Slice are in unnamed module of loader 'app')

2. Slice<Object>

Slice<ChatMsg> findBySessionId(Long sessionId , Pageable pageable);

Caused by: java.lang.IllegalStateException: Method has to use a either multi-item reactive
 wrapper return type or a wrapped Page/Slice type; Offending method: public abstract 
org.springframework.data.domain.Slice 
com.ifx.account.repository.ChatMsgRepository.findBySessionId(java.lang.Long,org.springfram-
ework.data.domain.Pageable)

Is previous example in a incorrect way? Alternatively , what should i do in order to troubleshoot?