I've been using AmbientOcclusion for almost three weeks, no problems until today. I have multiple scenes set up. Most scenes render OK, but some scenes render mainly white. I've turned off the other extensions – no change.
iMac Retina 5K, 4GHz Intel Core i7, 32 GB 1600 MHz DDR3
AMD Radeon R9 M295X 4096 MB
(video driver update fix not applicable to Macs)