samsung s5 green led lights up at lockscreen even though no notifications?

[AC Question]

the led will light up once i lock my phone and continue to blink (long blinks). the problem seems to be resolved temporarily by restarting the phone, but it starts all over again after awhile... my lockscreen just has DU battery saver as a fixed 'tab' in the notifications area. no new notifications come in yet the green led keeps lighting up.