Thanks for reaching out to us, updated the API version to the latest version or a stable version is very important to keep everything working well. Preview APIs are periodically deprecated. If you're using a preview API version, update your application to target the GA API version.
Since you are using a preview version which is not GA and updated, have you already migrated from Form Recognizer to Azure AI Document Intelligence as below guidance?
Please take a look to see if this is related to your issue, please let us know how it works, I hope this helps.
-Please kindly accept the answer if you feel helpful to support the community, thanks a lot.