Did the plant receive lots of nitrogen recently? If the N:S ratio is high, amino acids will build up and attract aphids. The spray will set them back for a while but they will keep rebouncing.
I am now more inclined to the opinion that plants getting balanced nutrition are healthy and pest free. Here is what John Kempf talked about aphids
https://permies.com/t/146343/prevent-manage-aphids-insects-managing
Although I don't have experience of adding S/Mg/B to get rid of aphid infestation, I had the other way round. Once I made organic liquid fertilizer from some sick looking plants and used on my healthy ones. Within a week, all had attracted some sorts of sap suckers on corresponding hosts! Lady bugs showed up later to clean the aphids up but the plants already lost quite some growth potentials.