I'm on the latest beta (4.8.931)
Still get occasional lock up when I go into Guide (no navigation buttons work then after a few seconds it exits to OS)
I've have also noticed that sometimes if I've had subtitles on but then turned them off, if I go into Guide and then back to Live TV the subtitles come back on again.
I can't get either of the above to repeat on demand so it's not much help I know, but thought I would report anyway. All on Nvidia Shields.