In order for Docusign to recognize PDF form fields, the fields must be configured as printable. The form field properties 'Visible' and 'Hidden But Printable' support the Docusign conversion process. More information about send a PDF with a Form fields is here: https://support.docusign.com/s/document-item?language=en_US&rsc_301&bundleId=gbo1643332197980&topicId=vhr1578456560761.html&_LANG=enus
Please check the above and if it doesn't solve your problem, we suggest initiating a support case with Docusign for further troubleshooting. Here's the link to open the support case: https://support.docusign.com/s/articles/How-Do-I-Open-a-Case-in-the-DocuSign-Support-Center?language=en_US