With more trial and error I believe I have found the issue.
If the form has google recaptcha v3 enabled, it doesn’t pass the submission on to hubspot (although it does successfully send the submission via email). If I remove the recaptcha v3 OR change to recaptcha v2, the form passes the submission to hubspot.
Is this a known issue regarding recaptcha v3? Is there any way to make recaptcha v3 play nice with hubspot? I don’t like the UX of requiring users to check a ‘im not a robot’ box.