Possible issues with eDRX on Verizon

Using the nRF9160 on the Verizon network we are having some issues with eDRX.  Specifically sending data to the device from our MQTT server.  

We have configured a eDRX interval of 40.96 seconds with a PTW of 1.28 seconds.  What I'm seeing is that the socket from the device to the server remains open and we can send data in that direction with no issue.  Server initiated messages are not reliably delivered, and when a server messages is not delivered it s breaks the server to device connection so any subsequent MQTT publishes from the device do reach the server, but the ACK does not reach the device.  If we close/open the socket then communications resume. 

We tried increasing the PTW to 5.12 seconds and that seems to improve things somewhat, but we are still seeing the same issue. 

Also I'm finding that if a server message is initiated during or right after a eDRX cycle, on the following eDRX cycle the nRF9160 does wake up for the ~9second RRC timeout (as seen on a current meter), but the message is not received and the socket from the server to the device is broken.  

We are working with Verizon on this issue as well, but they are indicating that this may be a nRF9160 issue.  

Any feedback on this use case/configuration?