Graph style "lines" changed to "points" after modify telegraf interval

I have one Graph to display temperature and recently I modified interval in telegraf (from 30s to 60s) for related input plugin. But now grafana display new data as points instead of lines.

It seems Grafana think there are NULL values, I can set Connect null values = thershold, that can fix Graph, but I also use Inspect > Data > (Download CSV) and there are empty records.
How to solve it ? I’m using Grafana v8.4.4