Well, this can be because your Foobot is not posting anymore. To check, have a look at Foobot: is it glowing, meaning blinking slowly like it’s breathing? If the answer is yes, this is the reason for your empty charts, device isn’t connected to Internet anymore.
It might also be because your Foobot isn’t tied properly to your account, in that case you usually get only zero values on main view (with gauges). Best is to contact support to ask for a complete check-up.