Welcome to HVAC 101, you'll love this answer, LOL.
WHEN it happens, be there and be prepared to jumpmin and test the circuits with a meter to find where the interruption is.
Also, check burner and burner orifice for blockages (spider/web).
That is why intermittant problems are so hard to detect, you need to be there when it happens.
Some people are Humbly Grateful, while some are Grumbly Hateful.................... Which one are you ?