I am also facing this problem, but it happens all the time, not only after a extended idle time.
I have found this thread: Manual dashboard refresh on Kibana
And the answer redirects to an issue on github: https://github.com/elastic/kibana/issues/23329
It is for an older version of Kibana (6.4) but it is still open.
Does anyone know any workaround for this problem? It is very annoying 