The static graphs are generated by index.php on each page load.
The source from which the graphs are generated is a round robin file "populated" by a cronjob that runs each 5 minutes.
So, possible causes for static graphs to show 0:

• /opt/minepeon/etc/cron.d/5min permissions were changed (should be 770 minepeon.http)
• /opt/minepeon/etc/cron.d/5min/hashrate permissions were changed (should be 770 minepeon.http)
• /opt/minepeon/etc/cron.d/5min/hashrate was removed (look it up on github)
• cronjob was removed?