Works for me, looks like your internet might be slow, at least when connecting to this site, as I believe it works by running the code in the cloud and streaming the results to you. Or perhaps it works on the machine, not sure.
https://github.com/jprendes/emception (2021)
https://github.com/tbfleming/cib (2017)
https://github.com/kripken/llvm.js (2012)
I agree it would be great to see this repl running 100% in the browser!