Ok... so I have a phantom 4 advanced..  I updated everything and took it out for a quick flight..  it went up to 400 feet and said max altitude reached..   The other day I was out flying it and I looked down and it ws at 650 feet ???   obviously I brought it down right away ... and no it wsnt set to metric ..  I have the max altitude set at 400 feet.   anyone know why I cant set the max altitude ???   

After updates, many settings get set back to default values.
This is what's changed for you.
You need to set a higher limit in the app when the Phantom is connected.

With your drone, RC and app running, change your parameters to your piloting preferences.

Always go over the app closely after updates, to see if indeed, something may have been switched back to a common factory settings condition.

RedHotPoker

I agree, always check your settings after every FW updates.

Agree with the above, please set the maximum height in MC Settings.

I have had mine up to 402 feet.  I kept looking for the black SUV's to arrive, but they never did...lol.   I also had a helicopter fly close to where I live today.  He wasn't very high,  probably 5-600 ft.  They normally don't fly that low unless they are looking for someone or something.  Who knows.  I wasn't flying mine today.