That's probably an issue that Gumroad, the marketplace, should handle. Not sure whether they have any official ways to submit bugs, but there's this: https://help.gumroad.com/article/20-how-do-i-contact-gumroad

I can't think of a reason why altering the field navigation order would be done intentionally - bots and such should be able to just access fields by IDs/CSS selectors anyways.

Personally, i just looked at the free sample download requiring giving them my contact information (probably their way of delivering the products) and decided not to bother with that. In contrast, sites like itch.io (focused more on interactive content/video games and such) absolutely nails that part - free content can just be downloaded directly.