How to repair tsdb.HandleRequest() error Post http://<my-host>:8080/render: EOF

Hi everyone,
Recently, I get errors.
tsdb.HandleRequest() error Post http://:8080/render: EOF
Error: Alert execution exceeded the timeout

I know I can turn off the alert itself, by setting “If execution error or timeout” “SET STATE TO” “Keep Last State”, but I’m wondering if there is something further that I should investigate. Any thoughts?
Grafana ver. 5.0
Graphite 0.9.15