The information you provide has some conflicts. You say you were flying in Novice Mode. That mode restricts your altitude to 98 feet, your speed to 8mph, and your distance to 328 feet from takeoff point. There is no way you were in Novice mode flying at the distance and altitude you describe.
Losing altitude at a mile away gives me the impression that there was either a battery malfunction or low voltage triggering a landing or perhaps you ventured into an area where there was some severe interference like a main power transmission line, radio/tv broadcast tower, microwave/cell tower, etc. At one mile the angle of the aircraft compared to the controller at ground level is such that ground-based obstructions such as trees and buildings may block your signal or weaken it the farther you go from your control point when only at 425 feet AGL.
As far as the flight log, there is no better reason to record your phone/tablet screen display to your device during each flight and then delete it after a successful mission. In the event you lose your bird without a flight log to identify the last known location, the video on your device will give telemetry as well as the last camera view of where it was before going dark. In the best of circumstances that can have a happy ending with a retrieval.
I'm not positive but I think the flight log is saved on the phone or tablet device, not the controller. Did you check your Explorer Profile on your phone to see if the last flight was there?
I know its a moot point but for other pilots out there, if you are getting your drone and/or controller back from service/warranty work, its best to be patience and take 'baby steps' as you start testing the equipment for proper function and performance. It sounds as if your equipment had some major problems and issues to resolve in the repair process. Most vehicle owners who just got their car overhauled wouldn't take off on a cross country road trip without first making sure it was now dependable. The same applies, perhaps more so, with unmanned aircraft that can disappear ever so easily and hide anywhere.
I guess the last thought is someone might have shot it down or it was attacked by a hawk or eagle. You would never know at that distance.