After some more sleuth work with NVIDIA, we've discovered that this is happening because of a RANDR event. An X client is responding to the RANDR events and forcing it to this NULL resolution.
I checked what clients were running, and it's xfsettingsd causing this problem. If I kill xfsettingsd prior to turning on/off my TV it comes back at the right resolution.
After some more sleuth work with NVIDIA, we've discovered that this is happening because of a RANDR event. An X client is responding to the RANDR events and forcing it to this NULL resolution.
I checked what clients were running, and it's xfsettingsd causing this problem. If I kill xfsettingsd prior to turning on/off my TV it comes back at the right resolution.