It was a fairly nice day for Northern Illinois this time of year about 55 degrees, sunshine and very little wind, this was in contrast to the previous days that were snowy with bone chilling wind. Had completed two flights about 18 minutes each and was preparing to take off with the 3rd battery when across the screen a message "IMU calibration required". So I stopped and returned the bird to the workbench and connected the RC and the bird to the Assistant software running on a Mac. As soon as I was connected, DJI had an update waiting, read the details included in the update saw nothing evil so I updated. Now everything was at the latest versions. When I went to check IMU status everything' was OK, but since I had had the error, I decided to do an "advanced IMU check. Took about 3 minutes but I got the green check when completed. I had already checked the RC in both programs because I had noticed a yellow LED on the version 2 controller, so I calibrated the sticks in both programs. While I was in the Assistant Program I changed the maximum height to 400', reason being I'm near the 5 mile radius of an Airport. I figured with all the "idiot" drone pilots you read about in the news I didn't want to give anyone any reason to report me to the FAA. Before I get into the details of my sad story, my bird purchased in early June of this year had been moded with FPVLR Stage 2 bird side antennas along with the RC antennas. Which are fantastic by the way. I would've normally flown with a UAV Tracker, but it has failed so many times, I stopped using it. And because of the glowing recommendation from DirtyBird on the Flytrex Live 3G, I'm now awaiting its arrival. So against better judgement I'm flying without a tracker. So now for my third flight of the day, since I had upgraded new software, I figured I would recalibrate the Compass and GPS before takeoff. Everything checked out fine, took off with 9 Satellites. Went up about 150' , she is hovering steady and the controls are very responsive. I started flying N/W at about 300'. Got out 1735' and I get a notice on the screen the "Maximum Altitude reached" even though the Altimeter reading on the display said I was at 470' It was right after this that I get "Phantom Connection Lost" and the video freezes. This was very unusual because I've been consistently flying at about 3000'. Since right prior to this I had lost line of sight I now wait patiently for the "Returning Home" to display. After what seems to be an eternity I realize it is not going to return on it's own even though It has alway returned in the past so I'm very concerned. The display shows the coordinates when the connection broke and in the .app I used "Find My Phantom" to get the location on a map. After securing the property owners permission to search the area and the better part of three hours with three people the bird was nowhere to be found. I made the assumption that the bird must've suffered a major power failure in that both control and video were lost at the same time. My question to anyone reading this Do you think the software upgrade could possibly have caused this, and has anyone had any luck withe the "Find my Phantom feature in the .app? Guess I just got an email from Flytrex saying my Flytrex Live had been shipped and was on its way. Story of my life a day late and dollar short. Thanks for reading.