Although designed to protect circuitry from 'latch-up' or incorrect operation during power dips, 'brown-out' protection systems can sometimes be the cause of equipment suddenly "rebooting" for no apparent reason.
Such circuits are designed in by well-meaning engineers, but are often far too sensitive for their own good. A well designed brown-out detection circuit is meant to predict such a situation is approaching and process it accordingly. However, as is often proven with weather prediction, it has a high chance of failure.
Such failures are often found when employing "Take-Over Power Supplies" or TOPS (as opposed to Uninterruptable Power Supplies). A TOPS is designed to be fully ready and as soon as a mains failure is recognised it disconnects the load from the mains and takes over the function of supplying power.
During this take over cycle it is highly possible for brown-out detection circuits to trigger and totally work against the whole purpose of having a TOPS in the first place. Even genuine UPS systems that are phase locked to the incoming mains can, during a power failure, suddenly shift phase sufficiently to trigger a brown-out detection circuit.
If such faults are detected then contacting the manufacturer is a first port of call.