Emails Throttled - RL000002

Our organization sends tens of thousands of emails a day on behalf of a client of ours.  These are legitimate, opted in transactional and marketing emails.  We recently spun up a second static IP for them last week; prior to and including Monday, July 3rd 2017 we had no issue sending emails to comcast.net customers.  However, since Tuesday, July 4th 2017 we have been throttled severely (approx. 10 emails an hour if that...)  and the SMPT code we are recieving is as follows:

451 4.2.0 68.69.14.27 Throttled - try again later. SyEWdGKFD38hOSyEbdIFU1 Please see http://postmaster.comcast.net/smtp-error-codes.php#RL000002  192.168.201.127 mx2.comcast.net

(Note, this is for our first IP (68.69.14.27) and we are also getting this code for our new IP (68.69.14.12)

Having seen this message we went to http://postmaster.comcast.net/smtp-error-codes.php#RL000002  and contacted Customer Security Assurance at 888-565-4329 where I spoke to Mark who verified that neither of these IPs were on a blacklist nor had a poor reputation through Cloudmark.  After some troubleshooting he escalated the ticket (NA249235945) and said we should hear back withing 24 hours.  We have not heard anything yet.

Can you please assist us in finding our why we are being throttled so heavily, as this is severely impacting our clients ability to conduct legitimate marketing and transactional business with their Opt In clients and we are not seeing any similar issues with any other major providers.  Thank you.