(May 5, 202): We are aware of the situation where error message "Invalid parentId. Subform requires parentId to be non-zero" is showing up after syncing records. Our development team is actively looking into this. In the meantime, this can be remedied by performing multiple syncs. Please reference our helpdesk article here. If multiple syncs does not resolve the error, please reach out to our support team at firstname.lastname@example.org and submit an Emergency Database Upload.