I resolved the Phantom 4 maximum flight altitude limitation after your latest firmware update by taking the following actions, I would suggest posting this procedure on your forum for non-technical people as it was trial and error for me to figure out, with no good instructions or notifications from DJI:

1- Logged aircraft onto computer an used DJI assistant 2 to refresh the firmware, then rebooted the aircraft. Logged back the DJI assistant 2 to make sure the firmware installed correctly. Firmware installed ok.
2- uninstalled the DJI GO app on my IPAD 4 mini.
3- Re-installed the  latest version DJI GO app from the apple app store. The latest version addressed a software bug probably related to auto activating the latest firmware with FAA geospatial updates. Logged onto my DJI account thru the DJI GO app then started the aircraft. Changed units from metric to imperial.

Problem solved

You also have to have the latest version of the go app or flight limitations will not be unlocked.