The Rest API, when using a date filter with select:-1, is not returning data for the current calendar month.
&interval=monthly&filters[]=time:select:-1
The filter operates on the currently available data. For example, if you apply select:-1 in October, but the latest data for the customer tenant is from September, the system will return September's data, not October's.
As a workaround, you can use the filter option below, passing YYYY-MM in the select parameter to retrieve data for the desired month.
&interval=monthly&filters[]=time:select:2014-12