If you flashed to any leaked build (5.5.893leak - 5.7.893 - 5.8.894) you will not be able to install OTA updates as of right now, It Will fail.
To revert back to stock, use this thread here :
R3L3AS3DRoot and 43V3R root for the BIONIC v2.1 You can not revert back to the stock Kernel/Radio if you have installed a leak update.
There currently is nothing you can do to go back to the stock Kernel/Radio.
As for the factory reset...All that a factory reset does is wipe your phone's data/cache. It does not revert back to stock.