Did the line contactor actually open and then close again? The system's down only five seconds? How far into the show is this occurring? High Reactance or Switcher?

If the contactor is opening then the problem is likely interlocks, door or air. I'd suspect air interlocks first, especially the exhaust. That bracket is designed to be bent up into the stack at about a 30-degree angle, to be sure it's in the air flow of the exhaust pipe. Has it been really windy? I've had situations where outside wind created so much back pressure it would close down airflow intermittently. Other than that, be sure the intake air flow switch is clean and fully pulled in by a clean impeller on that top fan of the console.

Door interlocks are a possibility. If equipped with the magnetic interlocks, be sure the actuators are positioned correctly and the doors are fully closed. If it's an older console with the pushbutton switch, bend the bracket slightly to be sure the door engages the switch fully.

After that, it's wiring in the rest of the interlock circuit going back to the contactor in the power supply. It's not thermal because five seconds is too short a time too cool down anything enough to close a thermal switch again.

If the contactor's not dropping out, the lamp is the first suspect. Try and watch the arc, it would normally waver like hell before it extinguishes. Problem is that you'd be really lucky to actually see that, given it's still a rare occurence. You should see quite a bit of waver when it's running, if it's getting that bad. It could be a loose DC connection so check your DC cable connections, but I'd bet against that. It would heat up to the point where resistence is too high and you'd lose current flow, but that prioblem would occur at a rapidly increasing rate and not just once a day or so.

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It could be a goofy airflow interlock, maybe a door interlock, etc. If the igniter does not fire almost about one or two seconds after the bulb goes out, I doubt if it is the bulb that is causing the problem. It is probably an interlock problem. Do you have a stack airflow switch in that thing?