Please prove that statement with raw data (e.g. query inspector). I bet there are no data from PostgreSQL - they are just connected existing datapoints:
BTW you have heavy query, customize this for you needs:
SELECT
$__timeGroupAlias(timecolumn, $agg, 0),
AVG(value) AS "metric"
FROM table
WHERE
$__timeFilter(timecolumn)
GROUP BY 1
ORDER BY 1
