Alerts are falsely triggered when the query is grouped by day

Hi all, I am setting up an alert on Grafana, but the alerts are falsely triggered. Anyone know what might be the causing issue? Thanks!

As you can see from the figure, the alerts are triggered when the value is actually beyond the threshold. The actual value is around 2.5, but the alarm said that the value is 0.036.

Attached is my query. I took the difference between maximum and minimum value of each day.

max(SJV_MDW_109_WI_F950_DPFILT_PV) - min(SJV_MDW_109_WI_F950_DPFILT_PV) AS “DPrange”
FROM wide_data_package
ORDER BY $__timeGroup(t_stamp,1d)

My alert setting: