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I cannot seem to replicate the issue you encountered. I cloned your form and tried to create a Fillable PDF. I was able to create and download the PDF successfully.
Can you please try clearing your browser cache and your form cache to see if that resolves the issue? Here are a couple of guides that can help:
You can also check out this article for more information about Fillable PDFs: Fillable PDF - Everything you need to know about JotForm Fillable PDF Creator
Do let us know if you need further assistance.
We are sorry for the inconvenience this may caused you. This problem should be fixed now. We would appreciate if you could also test it on your side and let us know if the problem persists.