BTW. i love the look and simplicity of the Minera dashboard.
I have this problem where occasionally the miners will go down and the minera dashboard, and even the lighttpd test page will return a 404. I'm unable to ssh into the machine when this is happening and I can't find anything in the logs to indicate that something is going on, much less what.
I suspect one of the partitions on the SD card is spontaneously un-mounting periodically.
My solution is I have a monitoring service check the lighttpd default page every 30 minutes. If it doesn't find the normal text, it sends me an email which is specially labeled by a gmail rule. Then I have an IFTTT rule that checks for new emails with that label. The whole mining rig is plugged into a WeMo outlet and if there's a new email matching the miner being down, it power cycles the whole rig.
Byzantine, yet highly effective.
The wemo outlet also allows me to monitor the power consumption and remotely power off or power on the rig if needed so it's a neat thing to have.