Multiple error NO DATA

Grafana Graphite
1

Hi,
Recently I have a problem with constantly appearing errors like this ( NO DATA )

errors
errors721×593 53.8 KB

graph
graph1648×358 57.5 KB

Carbon
2x VM Cache and 2x VM relay, Metrics received ~350k

Grafana 5.3.2, carbons and graphite 1.1.x
any ideas? There is nothing in the logs.