isolated, intermittent, irregular, unpredictable, scattered, stray, periodic, fitful, spasmodic, endemical, more...

endemic, epidemic

random, irregular, intermittent, occasional, infrequent, spotty, scattered, isolated, more...

occasional use,   sporadically placed,   at random intervals,   not regularly,   in bursts,   one and off,   the occasional,   infrequent light,   (adj.) irregular,   often interrupted