When I visit kbin.social, I see new posts regularly. On other servers posts stay on the frontpage for multiple days. This is also true if I switch their sorting to “hot”. So that is probably not the difference.
What is kbin.social doing differently?
Kbin and Lemmy are different frameworks and have been written using different languages. After some hiccups initially, kbin seem to be more stable than Lemmy right now, including when it comes to frontpage sorting. But both are pretty new and are actively being developed. You can expect these issues to be fixed soon as the devs push new updates.