As far as I know, eHarmony's claim of the questionnaire and algorithm being based on science was marketing fluff from the beginning [1]. One of the founders was a clinical psychologist, but the only science I've ever seen them cite is just studies that they claim show eHarmony to be more successful than other dating sites (which might have something to do with the company's policy of outright rejecting users who are too depressed or too divorced [2]).

[1] https://www.bbc.com/news/uk-42546586

[2] https://www.arkansasonline.com/news/2007/may/22/no-love-lost...