There are issues on both the Kbin and Lemmy sides at the moment.
Lemmy released a new update with a bunch of fixes, but it seems to have caused other bugs. Lemmy servers with this update are becoming accidentally disconnected from everywhere else. They're working on a fix.
Kbin is a brand-new site (Kbin.social didn't exist in April of this year!). Ernest (our admin and the guy who made Kbin) has only been working on it "seriously" since January. When I joined Kbin in early June, there were just a couple dozen accounts here.
Poor Ernest has had a very rough month getting his fun little side project he put on the internet after a couple months' of work and scaling it to 100k+ users (and growing...). He's done an amazing job but the servers are maxing out. There's a big Kbin update coming soon, and the site will be on better servers.
The main issue is that there are 2 things happening at once on any fediverse site: it has to handle your local stuff (comments, posts, etc. made to Kbin.social) and it has to periodically sync (push/pull) the remote stuff from everywhere else and merge it into the local stuff. Right now, Kbin is focused on making it super-smooth locally at the expense of making syncs happen less often remotely.
This means it takes longer to send and receive posts from other fediverse services, but anything you do here will (usually) work first try without giving you an error. Once the big update happens in the coming days, sync times will go down and you'll get much fresher posts - assuming Lemmy fixes the issues on their end that have popped up.