One time we had no spark at two of the burners , after taking the stove top off, (it just lifts off with a good pull upwards) I found two of the wires had come off the contacts at the back of the knob.
Sometimes they don't want to light and we have to turn the knob 3 or four times, like 3x360deg to get it to light.
One thing though I notice at high altitudes it is harder to light.
The oven is another story