"The bulb is right for the fixture all the wiring is right" But is it tight? A loose connection anywhere in the circuit could cause some trouble... Including the contacts in the can to the lamp. In LV cans it is common that the socket can heat up making it progressively worse over time. A resistive or arching connection would artificialy raise the amperage and drop voltage to the lamp. (or viseversa)
And yeah, bad bulbs.... (cheap means expendable)