My Mavic Pro has been updating for over 45 mins now and it still says:
Uploading firmware:94%    Progress:28%

It hasn't frozen or come up saying there's an error like other people have mentiond so wasn't sure if it was a good idea to shut down or restart anything.
Any advice would be great, thanks

Hi, we're sorry for the inconvenience. May I know what method are you trying to use to update the firmware of your drone? I suggest you do the firmware update via DJI Assistant 2. You can follow the steps on the video tutorial below. If you have other concern, please let us know. Thank you.

Just shut down and do it again. I had it also. I also would recommend to stay with fw .300 or .200, the .400 causes a lot of problems with a lot of people.

Hi, like DJI Natalia mentioned, you can use the DJII Assistant 2 to update the firmware and for the additional information, this application can be downloaded using the link below. Please keep us posted on the latest progress. Thank you.

https://www.dji.com/mavic/info#downloads

Same problem with my Mavic Pro.  I'm using the DJI Assistant 2 to update firmware but it is taking a VERY long time.  I've aborted and re-started several times -- to make sure the laptop doesn't go into sleep mode or anything.  Once, I got to the end of the update process but received a message saying that the update failed because the drone battery was less than 50%.  I'm now into my 4th update attempt, and 35 minutes into it.  The DJI Assistant 2 says that I'm 46% through the process and the drone batter is about to fall into 75% power (3 solid green lights, one flashing green light).  Doesn't look like I will make it before the battery drops to 50%.  This is crazy.  Any suggestions?

Exact problem as CRdroneflights here.

Any solutions?