my first procedure would be to pull them out of where they are and try them in another fixture... the leds can fail, but not likely both at the same time.
I would be inclinded to say there is a wiring issue at the particular fixture that could probably be found by removing it and inspecting it for a loose ground or hot wire.
some fixtures have the wires rivited to the contacts, and Ive seen where these connections have not gotten tight enough in the manufacturing process, or loosend by the heat from an incandescent bulb that may have been in the fixture before...
it could also be a wiring issue upstream somewhere, but not as likely as the problem being at the fixture.