Dashboard No data / no requests to server

Hi guys, i spent a lot of time with googling, but without success.

I use plugin https://github.com/simPod/grafana-json-datasource and flask server for serving data…
(i tried plugin https://github.com/grafana/simple-json-datasource too but behavior was same…)

When i add new dashboard with grafana-json-datasource plugin, in network console in firefox i see request to my server and i see request in log of my server too.

But when dashboard is added i see only message “No data” and when i try to refresh data, request to endpoint /query isnt fired. In console i see only request to /annotation and my log in flask server is empty too. (request wasnt call…)

When i try section “Explore”, request to /query is called.

I am Grafana newbie and i don`t know if problem is in my settings, in external plugin or in Grafana.

Please, do you have any idea, where can by a problem?

Grafana version: Grafana v7.1.0 (8101355285)
Server: Ubuntu Server 18.04
App: Flask 1.1.2

Thank you for any answer.