I think we can identify quite a few critical theorists whose body of thought contained reactionary elements alongside the 'revolutionary'--if you define reactionary elements as working to solidify social power as opposed to break it apart.

-Heidegger, maybe not a critical theorist in himself, has been massively influential and foundational to Arendt, Derrida, Sartre, Camus, and many others, despite his anti-semitism and Nazism. You might say this is separate from his phenomenological work but there is an argument to be had over whether we should treat a problematic thinker's academic texts as existing outside of their existing life-story.

--Althusser and many other French intellectuals in the 'Post-Frankfurt School' era can be described as containing reactionary elements within their thought. They were so closely aligned with the PCF (French [Stalinist] Communist Party) that they denounced 68 as a bourgeois-student revolution, essentially trying to redirect a spontaneous struggle into established, ossified and bureaucratic forms of representation. (Similar things can be said of many Soviet thinkers, and the academic body of work which emerged in the USSR under Stalin's rule; scathing about capitalism, entirely soft on the power structures of the USSR).

--Finally, there are thinkers as varied as Andrea Dworkin, Jean Baudrillard, Albert Camus, who all have been taken to task for reactionary views re: gender, sexuality, race (not respectively/in that order). See Trans/Sex Work Exclusionary Feminism, Baudrillard's work on 'Seduction.' And the 'Meursault Investigation'. You might put these problems down to blindspots in these scholars' thoughts, the unintentional overlooking of oppression dynamics, but nonetheless their thought, whilst being 'critical', contains within it elements which forward a conservative agenda (for certain groups of people).