Just chiming in as another victim of this bug. Like others, all my savegames are currently broken and I do not wish to start my current 15 hours over. I was able to restart the client once and continue playing. I am currently in Caed Nua. I had the bug while in the area, restarted, got my companion back. After leaving to heal up, came back in, fought Maerwald and now the portrait of my wolf is just a white block. The first time it happened I did notice some lighting glitching out.