I have a Shinken installation with Webui2 et Graphite2 but I have a strange behavior.

Sometimes, the Webui and Graphite does not receive actualized data anymore. For example on the webui show a past time for the next check (eg: Next Active Check: 5h 21m 28s ago) and no more metrics are push to graphite. This is happening at the same time for all hosts and services.
But I still receive alert by email so checks still triggered successfully.
This is happen randomly after a few hours or few weeks.

Is someone have an idea what can cause this or which log file or debug option I can watch to resolve this?