What are the lights showing after the unit is no longer detected by the Drobo Dashboard?
Is the unit remained powered?
If the unit had shutdown or rebooted, check the light on the power brick whether it stays solid green or it is flickering / dimmed.
If it is the latter, try connecting it directly to a power source if not already. If the issue persists, it may have been a failing power supply unit.
did you get some solution for the same? I am facing the same problem in my drobo fs after I installed minidlna. only difference is mine does not disappear. It is taking forever to appear. It shows on my TV (only as root though). I fear I might lose all my data if i decide to reformat the device.