That's a Devpost thing I encountered as well. When you submit a new project to a challenge, you first create a project that is public in your profile. Then you go on to submit it to the challenge. If you back out of submitting it to the challenge, it still remains as a project in your portfolio. Or that is what I have experienced myself. The submissions gallery is only shown when the sponsor has chosen to show it (commonly after the deadline, but sometimes it can be before the deadline).