Leaky washing machine shut off valve from Sioux Chief

I installed a sioux chief ox box valve. i pressure tested my work and this valve after i hooked it up, no problems, after i finalized running the rest of my piping today, i tested first the cold, then the hot. worked fine, until i kept working the valves on/off to rid the system of air. now, the cold valve will not shut off all the way... did debris get in there? maybe some residual flux? the pic is the box i have.