Total value has wrong calculation

Hi,

I tried to use Visualization -> Legend -> Value total but i got right values only for no more then 2 day.
I am not sure if it problem of PromQL, Grafana ot smt else.
I have attached screenshot with Total column.

Prom expr: sum(rate(nginx_ingress_controller_response_size_sum{ingress!=""}[2m]))

Grafana v6.3.5