Thanks for reaching out to us for help. I cloned and tested the form and I was able to proceed with the submission without any delays or errors. Here's a screencast of my test submission:
As you saw, I was redirected to the external URL after clicking the Submit button which indicates that the submission was completed and accepted. Can you do a couple of test submissions again on your form? I've cleared your form cache as an additional measure. If the issue persists, try using a different web browser. If you're still getting the same issue despite doing all of these, can we do a test submission on your actual form?
Give those a try first and let us know how it goes.