Basically, it seems to happen with any screensaver that doesn't list Roku as the developer. Most often, it'll load the title splash screen then crash when trying to load the slideshow. I've tried National Parks, Sakura, B.P.O.D, Hawaii Collection, Tokyo, Spring Collection, Cherry Blossom that I can remember.
Model is: 4620X - Roku Premiere
Software version: 9.4.0 build 4200-29