Outlook Recurring Task came back uncompleted after few time taht the client mark them as completed and task in owa still not mark completed

Hi need help on this.

i got a client that is mail box recurring task keep comming up as not completed and got duplicated one complet and one is not in Outlook.

On the exchange side the task is always one day behind the one in Outlook.

Got any solution to that.

I try to flush ost file and get new one but problem still there.