In Hubspot, the Date of Birth default system field defaults to a single-line text field format when associated with an external form (which in this instance is Formstack), and not as a standard (epoch) date field format.
For context, this can be changed to a standard format only if there is no association with an external form. This of course does not prove useful when an integration is required.
Therefore, when integrated with a Formstack form that has a mapped date field (also in the standard epoch format) it can yield bad data within Hubspot due to the difference in formats.
A workaround to this would be to use a standard format date field in Hubspot concurrent to the date field in Formstack.
HubSpot Integration - Date of Birth Field
