for my moto bought at&t running nexus 6 the download was one of those that started downloaded and disappeared. I pulled sim restarted and nothing, I then backed up all to cloud reset phone to factory started without the sim in but WIFI connected and "voila" downloaded as before but continued to the installation, added everything back on wifi only, set up phone then, installed at&t sim. It has updated and all is good. I experienced no restarts or screen problems prior battery life has always been good and nothing seems to be changed aside from version and build at this time. It seems the AT&T sim is somehow the culprit to my disappearing download prior.