I created a new item via LLD, gathered some data, then opened Latest data graph and found that it shows data for 1 day, but item created only few minutes ago!
As you can see on screenshots graph shows non existing data while 'text mode' shows right amount of values.

What I did is 'Unlink and clear' template on host and then re-added template again. But anyway, 'text mode' shows correct amount of values.