Have you blocked anyone? There's a bug that causes certain threads, including your own, to not be visible to you outside your profile. It's caused by you blocking anyone at all iirc. Or maybe it's about blocking domains, I forgot the specifics, but try removing any and all blocks and see if that solved it.
It's fixed in the latest code iirc, but there's not been a stable release yet that incorporates the change.
Additionally, and I have no idea if this is related, I cannot send direct messages to anyone outside of kbin.social
This is correct, direct messages only work on the same instance currently. If I remember the previous discussions about it correctly, this is intentional for some undisclosed (or lost to time?) reason currently. Like, the developer has specifically added code to cause this behavior, I assume because there were worse issues with it.