My understanding is that there were some issues with the site after maintenance this weekend and it is actively being worked on! Unfortunately, if it is on the code.org side of things there isn’t much you can do to “fix” the problem.
Depending on your school population, you might want to consider offering a time after school today for students to get help with submitting. OR if your school is supportive, maybe suggesting your students get out 20 minutes early from their last hour to meet you in a lab/classroom to do it. As long as it is fixed by then, you should be good to go.
I know it is stressful, and less than ideal, but I am just brainstorming other solutions.