The switch mode power supply often has a minimum output, so one lamp blowing can cause the power supply to close down, so you can test supply in to the power supply but not so easy to test supply out, also some dimmer switches also can auto disconnect if load too high, so best to replace with standard switch until fault is found.
I assume your using quartz halogen as you say looks OK and nothing to see with LED lights, but at some point you will be forced to go down the LED route, so it may be better to do that now rather than latter.
The whole reason for extra low voltage lights (230 volt AC is low voltage) is so the filament is thicker so will last longer, once you move to LED low voltage is often a better option, as you can often get smart versions which I have not seen with extra low voltage.
So you need to consider if best option is to ditch extra low voltage and move to low voltage. Even if at some time in the future, one has to question changing a high frequency output switched mode power supply for a smooth DC switch mode power supply if in a short time you will want to swap the whole fitting.