Singlestat Math plugin not giving data for 30days of data

What happened?
When I use Singlestat math plugin and select 30 days in dropdown it not render correct value. So I am cliking the plugin edit option and just clicking on the Query text box the plugin refreshes and renders correct value.

What was expected to happen?
When I select the 30 days or 15 days the value should automatically displays in the singlestat math plugin , I should go to edit options and refresh it .

Steps to reproduce the problem:

  1. Create a single stat math and give query formulas .
  2. Select from drop down as 2 days or last 24 hours --> correct value will come.
  3. Select from drop down as last 15 days or 30 days --> value will not come.
  4. Click >Edit in the single stat math plugin and just click in the query box and display box value refreshes and populate.

Version numbers (grafana, prometheus, graphite, plugins, operating system, etc.):
Grafana - 6.7.3 and 7.1.0
prometheus - 2.7.1