I have a light circuit with 6 x 3W LED lights (all the same) on it and 1 transformer per pair of lights. When I switch them on there is a slight delay of about 1/10th of a second before the last 2 lights come on. Not a problem in itself, however, the transformer on these last 2 lights has blown twice now for no apparent reason. Transformers are 230Vac to 12Vdc 12W. Any suggestions?

Assuming you installed a new transformer after one "blew" because it failed, there could be a short circuit in one of the lights, the wiring from the transformer to the lights, or perhaps the LED board itself.

That was my first thought, however, the lights have been changed and although the wiring is awful it all checks out. What I don't understand is that time delay and why it works for 2-3 months and then blows.