Ongoing Throttling Issue (Error RL000010) – Request for Support

Dear Xfinity Support,

We are seeing repeated throttling with the error:
451 4.2.0 Throttled - https://postmaster.comcast.net/smtp-error-codes.php#RL000010

Our emails comply with all standards (SPF, DKIM, DMARC), and we are a Validity Certification member.
Not sure why this continues—would appreciate your help in resolving the issue.