I was looking at the DS log again today and I saw this: Iray INFO - module:category(IRAY:RENDER): 1.0 IRAY rend info : Rendering... WARNING: dzneuraymgr.cpp(261): Iray ERROR - module:category(IRAY:RENDER): 1.3 IRAY rend error: OptiX Prime error (Device rtpContextCreate): Unknown error WARNING: dzneuraymgr.cpp(261): Iray ERROR - module:category(IRAY:RENDER): 1.2 IRAY rend error: CUDA device 0 (GeForce GTX 780 Ti): Scene setup failed WARNING: dzneuraymgr.cpp(261): Iray ERROR - module:category(IRAY:RENDER): 1.2 IRAY rend error: CUDA device 0 (GeForce GTX 780 Ti): Device failed while rendering WARNING: dzneuraymgr.cpp(261): Iray WARNING - module:category(IRAY:RENDER): 1.2 IRAY rend warn : Re-rendering iteration because of device failure WARNING: dzneuraymgr.cpp(261): Iray ERROR - module:category(IRAY:RENDER): 1.2 IRAY rend error: All workers failed: aborting render WARNING: dzneuraymgr.cpp(261): Iray WARNING - module:category(IRAY:RENDER): 1.2 IRAY rend warn : All available GPUs failed. Iray INFO - module:category(IRAY:RENDER): 1.2 IRAY rend info : Falling back to CPU rendering.

You can view the log file by going to Help > Troubleshooting > View Log File

So now I'm trying it with Optix Prime Acceleration unchecked. You can uncheck it in the Advanced Tab of the Render Settings pane. So far, it's working but I'll try to make sure that solves it.