Upgrading one of my Flint 2 MT-6000 from v4.7.0 to v4.7.4 has caused the GL-iNet WebUI to break/stop working. The Luci interface remains to work fine, as does everything else like ssh etc...
Yes GL GUI I couldn't get to at all and it appeared as if it wasn't even running on port 80. I performed the update via the GL GUI Update page and it auto downloaded, installed, and then rebooted.
I managed to get it back up and working by performing the following...
In Luci => System => Backup/ Flash Firmware => Flash new firmware image (Flash Image..) (Upload firmware downloaded in step 1)
Select save all settings
Let/Allow luci to reboot the router and come back up naturally
The GL GUI now works again and all my settings were restored.
In hindsight and in future I will
Note down the current working GL GUI firmware version
Ensure I have both files of the new updated firmware version and the existing firmware version in step 1
Backup config using Lucu => System => Backup/ Flash Firmware
Perform upgrade
All these steps will allow a total rollback in settings and firmware should something break like it did....
Everyone should do this else you will have to reapply all settings manually (from memory if you've not recorded them down anywhere) after performing a factory reset or UBOOT reset ie Not fun...