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I cloned your form and did a test submission but failed to reproduce any problem submitting the form.
To ensure it's not a unique issue on your form itself, I had to do a test submission on your actual form too. This was how it looked like from my perspective:
You would notice the form submitted successfully and worked as intended. If you could tell us how to replicate the problem, we can start looking for a resolution.
For the time being, please give it another try and let us know if the issue persists.