I think this may be a classic case of trying to over-engineer a relatively simple problem. In the real world, almost any filter will do something and trying to be very specific about what it has to eliminate when the cause isn't quantified is pointless. Unless the cause of the problem can be identified, the best strategy is a general purpose filter so lets look at what it has to do:
1. let the 24V AC pass through with as little difficulty as possible,
2. block as much of every other signal, assuming it is the interference, as possible.
A narrow band filter, centered on 50Hz would be ideal but also very bulky and very expensive. I'm thinking here of lots of large iron-cored inductors and capacitors, not in the slightest a practical solution.
So lets look at what is different between the wanted power and the unwanted interference. There are two parameters, voltage and frequency that will be different. It is unlikely to be an under-voltage or increase in the 24V that causes your fault because you would see it in other equipment. Far more likely is a rapid spike created by some external inductive load being switched on or off.
Spikes can be eliminated by two methods - by clamping or by filtering and often both are used. The problem with a clamp is what to do with the excess energy it has to absorb. Imagine this scenario (don't try this at home!), you want a 5V supply from a car battery so you connect a 5V Zener diode across it. The result is a puff of smoke from where the Zener used to be because it tried to sink many many Amps from the battery to limit its voltage. However, if you had added a suitable resistor in series with the Zener it would drop the excess in the resistor and give you the 5V you wanted. The same applies to clamping across 24V, usually a MOV would be used instead of a Zener but the principle would be the same, it still needs something in series to take up the difference between the actual voltage (with the spike) and the 24V you want. You have to be careful if you use a resistor because it will also limit the current to your load. Also note that 24V is probably an RMS voltage so the natural peaks will be about 1.4 times higher and you don't want to clip those off as well.
A better solution is an inductor and capacitor filter, it will have increasing attenuation as the frequency rises so the 50Hz, being low frequency is relatively unhindered but anything with faster rising and falling edges must, by definition, contain higher frequencies. Remember the reactance (= resistance to AC) of a capacitor falls as frequency rises and the reactance of an inductor increases with frequency so by adding C in parallel and L in series make passage of high frequencies harder in two ways in a conventional line filter.
The bottom line is that ANY line filter is better than none and you have to make some compromises between complexity, size, cost and performance. The filter you pictured will still work at 24V and you can still use it. The only thing to note is the MOVs are probably rated for 275VAC clamping so at 24V it's very unlikely they will ever operate, you would have to change them to 27.5V ones to get the same protection.
I would question where your 24V comes from, if it is dropped by a transformer, it may be more advantageous to use the original filter on the line side of the transformer.
Brian.