HubSpot has a few limits in place regarding merged contact records and form submissions for contact records:

1. Contacts are limited to 250 linked identities (vids) per contact.
   • If you try to merge two contacts, and the resulting contact would have more than 250 identities, you will get an error.
2. Contacts are limited to 1000 form submissions. Submissions that would take a contact over 1000 submissions will be dropped completely.
   • The form data will not update the contact record.
   • The submission itself will not show up for the contact record (either in the 'form-submissions' data from the Contacts API or in the contact's timeline).
   • The submission will not be evaluated for list membership or workflows.
   • The submission will not appear in the submissions list for the form viewing the form in HubSpot.

If you find that you're exceeding either of these limits because of testing, we'd recommend deleting the test contacts, and creating a new test record.  Using the same email address in the new contact would not restore the originally deleted contact, and any form submissions with the email would be associated to the new record and not the deleted record.