No, it's not on purpose. They're both large sites moving a lot of content back and forth, and the most recent Lemmy update significantly changed some elements of how it works, highlighting some resource management issues.
Things are just a little unoptimized right now, and it's a period of strong growth.
The only thing that shouldn't be syncing is down votes, as kbin doesn't federated down votes.
They will. These services just have never experienced as much traffic as they have the last few days, and things that work fine when you have a couple of thousand active users don't always hold up to larger scales.