Is this a Cloudflare problem? Without any error messages this may as well just be a Fedia bug. Every other Kbin user seems to be posting comments just fine.
the client is javascript after all
How edgy! It’s written in Typescript, though.
Best advice I can give you is to open up the dev tools and look for the exact error message that Kbin is hiding from you for some reason. Also do the usual checks (disable adblockers/all addons, try another browser, etc) for browser related issues.