There’s no message button on my user card (?) - that thing appearing when the avatar is clicked. Because of that other users can’t start new conversations with me. So far I don’t know if it affects conversations started by me. It’s the first time I know that a non-moderator tried to send me a message since November '18, and the first time since my username change including moderators.
Edit: If I send a message to someone they can normally reply.
Bump, because it seems that the problem persists 
No button still. I don’t see it affecting other people with their usernames changed.
As an admin I don’t see anything in your account that would be off. So no idea why that would be! 
Ok, I’m somewhat dumb. Only after reading your reply I finally thought about googling the problem (because hello, there’s plenty of other Discourse forums) aaand… found it. So, thanks for helping me start to think.
It’s just a damn setting. Preferences > notifications > messages > allow other users to send me personal messages. I’ve disabled it when I left in 2018 and then forgot about it when I got back 
