I did another experiment in my normal running system. Once I change the display language from English to Chinese, the webUI goes to blank immediately....
Then I delete the Chinese language XML in tools and re-download from CA, the same problem still exists.(Does anyone know how to change language in command line so that I don't need to reboot in safe mode to change it)
It seems like a bug cause I never find kinda of problem before 6.12.4...