Problem with rear led lights

OK so Ive had the rear led lights on for a few months now with no issues. When I first fitted them I noticed that they only worked when either the lights where on but no key was in the ignition or if the engine was running. If I tried them with the key in and the ignition on but no engine running then 3 leds would fail after a few seconds on the passenger side cluster.

I could live with that so I was happy enough......

Tonight Ive noticed that now they only work if the engine is running. If the engine isn't running the same 3 leds fail after a few seconds.

I really need some advice as sending these back to the supplier, ie the USA would be a right expensive ball ache......

Any advice guys?

My car is due for a MoT in a few weeks time. Will this make it a fail? Or do they test the lights with the car running? Not all the leds go out, 3 leds out of I think about 8 go out with 5 staying on so there is still light so..........

Right so quick update....

Used the car tonight, got home and thought id check the lights and they worked? No engine running, just the switch on and no leds failed.....

Im wondering could it be a power thing? The car was stood yesterday for a day or two when the lights failed, now there working could it be because ive used the car? The batteries not failing but leds are a queer thing sometimes so?