One way to troubleshoot this is to go into graph display tab and check Points checkbox.
This way you can see that that there is indeed data there. But still why is there no lines between them?
The reason for this is that Elasticsearch and InfluxDB has a group by time feature where data is grouped into buckets. If there is no data in a given time bucket a null value is returned. This null value can be good to return as it can indicate a period of missing data. you can control if a null value time buckets should be returned or not by changing fill option in InfluxDB or the Min Doc Count option for Elasticsearch.
Still why no lines? There are no lines drawn as the Graph panel will not draw lines between values if there are null values in between. This can be important otherwise section with missing data could be hard to spot. You can change graph option Null value in display tab if you do not care abut this.
The root cause of the problem is however not the null values but the fact that the group by time interval is lower than the rate at which data is written (data collection frequency). So if you only write to your time series store every 10 seconds you do know want the group by time interval to go below this value.
In the data source edit view.
you find a global data source option where you can specify a lower limit for the group by time interval. Set this to >10s if you write every 10 seconds. You can also set this lower limit in the group by time interval option below your queries in the Metrics tab.