I just downgraded my Mavic to .0400 and had in hang at 86% in the DJI Assistant app.  Suspecting a failed reboot due to the fan not functioning and it getting hot, I decided to try powering off the Mavic and powering it back on.  I then proceeded to close the DJI app and restart it, and then the update started at the point where it left off and completed shortly after.

Hope this solution helps someone else.

Xaman1 - What was the reason you downgraded to .4?

NFZ garbage that I don't trust to not drop my drone in a lake like has been reported on here, and the fact that it from all reports seems to be the most trouble free.

In addition, you will not be able to downgrade in the future so you better get it while you can.  They are going to make your drone worthless it seems soon.

https://www.suasnews.com/2017/05 ... drones-next-update/