Not OP.

1. I’m seeing this on kbin, not mastodon, so federation is working as expected.
2. DMs don’t work very well cross service, AFAIK

Ah I tried searching for your dm/ reply but I didn’t see anything from you! However, today I got someone replying on my mastodon post from Kbin. I still need to figure out how to cross post here from Mastodon and vice versa. Thanks for letting me know that this is doable :)