We use Hubspot quite a lot for onboarding purposes in our operation.
Customers complain all the time about the Form because the mostly cannot fill out all questions at once and need to reach out internally first to find the corresponding answers-hence they would love to save the form and resume it later.
The issue is so severe that we consider to use another integration for that issue, which would be a little bit weird as we pay 50K+ for Hubspot and therefore expext such standard functionalities.
I have exactly the same concern...seems it has been raised for a couple of years now, with not response or fix. It seems like a simple thing that we all take for granted right, but they have yet to acknowledge that..