the problem when refresh Webi report in IPAD

Hi.   Experts.

  I have a strange problem that confused me,   After refresh my webi reprot in ipad, it turned from chart into table!   webi connected direct to BW bex query.  Any  idea about that? my  BI APP  version is 6.1.20.16(493559)，BO version is 4.1 SP3.

Thanks.