I say you swapped dimmer so not that, so it would seem likely a wire is dislodged, it is a problem with the electronic transformers that they don't have through terminals, so some where the wires need to be joined, ideal is something like this
where the cables are clamped, however in the real world more likely something like this
wrapped if your lucky in tape.
Given the rest seems suspect, think very likely a wire has worked lose. The electronic transformers you show are not simple transformers, they also control the output voltage as with a quartz lamp it is important to get maximum life that the voltage is spot on, too high as you will likely realise the filament will rupture, but also too low and the active material tungsten is deposited on the quartz envelope instead of back on the filament turning the quartz black and reducing lamp life, so quartz lamps should not be dimmed, they often are, but it reduces the bulb life.
7 x 50W = 350 watt or often called 350 VA that is some 1.5 amp at 230 volt which is a lot for lighting, in the main lighting is a total of 6 amp as ceiling roses and some switches are often only rated at 5 or 6 amp, so although permitted up to 16 amp for lighting, in real terms normally 6 amp is the maximum, so the dimming switch may have been overloaded and also the protective device may have been overloaded. That is fuse MCB or RCBO with the latter some makes you need to switch off to switch them back on, and they are designed so they can't be forced on, so some times they can look as if on but are not on, you can normally feel when they are faulty, you feel the resistance to switching on drop before latched on, so switch a good one off/on to feel what it should feel like, then try the faulty circuit to see if it feels the same.
The lamp you show comes in 10, 20, 35 and 50 watt, in fact there is also a 75 watt version although not often seen, your electronic transformer is rated 20 - 60 VA so it could have very likely originally had 35 watt lamps, or even 20 watt with no dimming switch, often dimming switches auto close down with overload, so worth removing some bulbs in case dimmer switch is overloaded.
I have seen where 10 watt lamps were originally fitted using a 60 VA transformer to supply 5 lamps, and since the bulbs look the same, 50 watt have been fitted in error.
The idea was to heat the room with the lights, not a bad idea as it goes, radiators provide back ground heat and heat the air, and the lights boost the temperature perceived with radiant heat which the wall thermostat or TRV will not measure, so instead of heating room to 20°C you heat room to 18°C and the heat from lights makes it feel like 20°C when switched on, so since the air is not as hot, air changes loose less heat, so it saves energy by using quartz lights in doors.
The problem is when you only want light, there is no way to stop having heat as well, so with a modern house we use programmable wall thermostats and TRV heads and LED lighting, you can debate which is best method, as it takes longer to heat air than to use radiant heat so then you get geofencing and occupancy detection controlling the heating, so it gets warm before you use the room, which the lighting did not require, however also LED lights tend to last longer as well, so they get rid of the chore of changing light bulbs.
In the main 12 volt lights were used as the filament was thicker and so lights lasted longer, however rather defeats the whole idea if a dimmer switch is fitted, and in the main LED lights there is no advantage using extra low voltage (12 volt), low voltage (230 volt) is simpler and easier. So now may be the time to consider moving to LED, and swap G5.3 to GU10 lamps, they are still MR16 size, but 230 volt. Note MR16 refers to having a multifaceted reflector 16/8th inch across, it does not refer to voltage or bulb base. Since LED lamps often have no reflector non are really MR16 they are just compatible. Also you can't get LED lamps with G5.3 base at 20 watt, and in the main they are 50 Hz rated, so you can't swap without also changing or getting rid of the power supplies (electronic transformers) you have.
The electrical lighting trade seems to have a problem with definitions and names, when ever a new produce is released, instead of giving it a new name, they add the word "electronic" to old name, and also have big writing on packet saying 50 watt with much smaller writing saying "equivalent to" and the lamp is really 7 watt, and replacing standard tungsten with quartz without saying not suitable for dimming, so it is like a mine field trying to work out what will work with what.
I have nearly swapped all tungsten for LED because don't like changing bulbs every couple of weeks, had one bad tube with LED when it only lasted 18 months but other than toys not had to date a LED bulb fail, and I use cheap B&M and Lidi bulbs. Think about it before spending out more money, is it time to change?