Hello Filipe,
Good day!
Unfortunately, the tracking isn't sufficient enough to understand the actual reason for the BULK API failure.
I would request you to share the steps needed to reproduce the error? Include the endpoint, full request and response of both (Submit and Poll operations), details of the API setup or environment.
NOTE: Don't share any private credentials e.g., access token, developer token.
Parallelly, you can step through this checklist and provide on this Bing Ads API documentation (https://free.blessedness.top/en-us/advertising/guides/handle-service-errors-exceptions?view=bingads-13#contact-support) the results to the support team.
Also, here is the documentation explaining how to Upload a Bulk File and Upload Best Practices.
Regards,
Manoj