Sure enough, just checked, Om was abandoned [2] and the person blogging about how great everything was is long gone [3]. This is the absolute definition of tech debt.
[1] https://circleci.com/blog/how-circleci-processes-4-5-million...
[2] https://github.com/omcljs/om
[3] https://circleci.com/blog/why-we-use-om-and-why-were-excited...
Umm, she left CircleCI last year after a 6-year stint. That's not exactly 'long gone'.
It seems like their UI is using next.js now and apparently it still has issues as per OP complaining about the run button behavior.
Frontend frameworks often get abandoned: jQuery, backbone, ember, angular, etc.
Seems to just be how things goes on the front end. This plagues not only the web, desktop and mobile frontend frameworks also all seem to come and go.