I have a serious issue when installing the latest fast ring build 10166. In few words, it downloads the build, prepares to install and the spinning gears are shown normally. But, at the end of the process in the spinning gears phase, the phone simply shutdown and not restart itself automatically. So, I turn on the phone manually, and after the Microsoft logo, it shows again the spinning gears, but this time they spin for about 1 minute, and after this time the phone restart itself, and if I don't turn off the phone, it keeps rebooting again and again in an endless boot loop state. I've reverted back to 8.1 and tried again to update to build 10166, but I had the same identical problem as before, so now I had to return to 8.1 and stay at 8.1, because of this serious issue.
I have a Lumia 435 CV IT and the revision of firmware is 02074.00000.15234.28005