Hello all,
I can't say how many times I've read various concerns regarding those who have upgraded to a new firmware only to then report negative results, while others not so much. However, reading post #17 by DroneB made me think further. I'm certainly by no stretch of the imagination an authority in this area, but that particular posting made me think back to what was once suggested as a prerequisite to performing a firmware change. It was strongly suggested that you
first format the SD card within the model before upgrading to a new firmware. To maximize success in this regard, this should be accomplished via the App. to essentially wipe clean any previous information which may then corrupt the new firmware version being downloaded.
I believe the steps DroneB performed to negate his issue was to wipe the slate clean and begin once again, a good move, but simply formatting the SD card first may accomplish the same results
As a matter of curiosity if there are any pilots contemplating an upgrade and would be willing to simply format the SD card beforehand via the Go App. It certainly wouldn't do any harm, and
MAY hopefully alleviate many of the issues experienced.
Just reaching for the stars here. 
As another POI, and once the download is completed, be sure to follow thru with other suggested download recommendations, eg.
1. Restart the radio controller & model.
2. Perform all necessary calibrations. eg. IMU, radio, camera, compass. etc.
All the best, and please feel free to make any further suggestions, or thoughts you may personally have to help alleviate this troubling process.