SMS Short Codes were being sent, but I was not receving them after a couple weeks of switching to XM from VZW. Worked with ComcastKenF (Thanks!!) to resolve, but the thread got marked as answered so i could not post the answer.
This came from the SMS aggregator. I am not sure who exactly lifted the SMS aggregator block (VZW maybe), but this seems to be standard practice for VZW after switching. I bolded the pertinent information.
"We are still working to resolve the delivery issue to mobile number ***-***-****. The messages are being successfully processed by our platform, but they are being failed by the SMS aggregator due to a deactivation request by Verizon.
When a client cancels service with Verizon Wireless, Verizon sends a deactivation request to all SMS aggregators requiring them to block all future attempts to send SMS message traffic for that number through the Verizon Network.
However, Xfinity Mobile is a mobile virtual network operator (MVNO) which uses the Verizon Wireless network to send and receive SMS messages. So the messages to this mobile number must continue to be routed though Verizon, but Verizon has ordered aggregators to block this message traffic. We are working with the SMS aggregator to get this block removed, but it not a quick process."
Hope this helps others trying to solve this problem... I have no idea if it happens to all transfers, or all short codes, or for all services. But it seemed to be known as a VZW practice.