It happens when the OP where you've posted a reply was deleted by the mod.
You didn't receive the notification because it wasn't your post that got deleted.
What was my mistake that it got deleted? Let me know, I'll try to sort it out, thanks.
Stop posting to spam threads.
Thank you, that helps. I don't usually follow comments so that means 15 threads got deleted? That quite a lot.
ps: locking this thread, as I got the answer.