I was under the impression that the electrical conductivity should increase initially, then begin to plateau, then fall past the saturation point for strong electrolytes. However, from this, I see that the conductivity of magnesium chloride does not follow this ( it is decreasing with increasing concentration) , BUT the data could be wrong though. Would someone mind explaining what I should expect when I conduct the experiment myself?
You simply started your data range at too high a concentration to see the initial increase. Semantic Scholar gives data for the conductivities of several aqueous electrolyte solutions at 25°C, including magnesium chloride. The strongly increasing portion of the magnesium chloride curve goes up to about 10%, which corresponds to about one molar (where your data happens to start).