How do I resolve RDK 03031 error

Got Xfinity installed recently; tv at main box as well as one tv on wireless connection are working fine, but the two TVs connected to regular cable boxes both stopped working now and are showing a message saying it can’t connect to the network and the code RDK 03031 in the lower right of the screen. I tried tightening cables, I got a box swapped at the local Comcast store today, I’ve restarted everything numerous times...no change.
Any advice would be greatly appreciated!