No, students are never blocked from submitting. If a student doesn’t reach validation, they can:
Go back to drafting and revise their work,
Try validation again (there's no limit on attempts), or
Send their work to you anyway.
The student decides when to send the work. When they do, you'll see the attempt they sent, including how they answered each question and how each validation factor contributed to the overall result.
A not yet validated result isn't a finding of misconduct. It means the submission is below the AI Use and Validity Threshold you set for this assessment, and it may be worth a closer look. Validate doesn't grade work or decide misconduct. That decision stays with you.