Data points not visible on grafana but present in DB after restart

I have a Influxdb-grafana setup with a python script periodically adding data to influxdb. All of these were setup on my localhost and the dashboard was running fine showing the data. But after a system restart only the points post restart are visible on dashboard and all other points are shown as "no data".

The data is present in influxdb. I could verify the query results by influx CLI. However when I use query inspector in grafana, I don't get any results. On exploring the result data of the panel it shows "null" for all the timestamps before restart.

I have read so much about it but can't seem to figure out what issue is this and how a system restart affected the visualization even though the data is present. I tried creating a new user with all privileges for the data source connection.

I also tried copying the entire DB just to verify but even copied DB doesn't show any data when there are about 500K points. Please suggest me how to fix this.

__Expected behavior:__
Points to be shown in Grafana since they are seen on querying,
No data loss

__Actual behavior:__
Data loss for one months recent data.
data is not reflecting on grafana
copied database doesn't work

__Environment info:__

* System info: Windows OS
* InfluxDB version: 1.8.2

Start by reproducing the behavior with InfluxDB 1.8.2 and Grafana on Windows, then compare the Influx CLI results with the Grafana query inspector before and after a system restart. Check the panel data for the timestamps before the restart and verify whether the copied database behaves the same. Done means historical points render in Grafana without data loss.

Written by the indexing model from the issue text.