Posting this experience here trying to help people.
Last week, my S4 mini duos hung when I was reading a web page on Chrome. System became unresponsive, I shutdown the cell phone put it to recharge and went to sleep. Next day, it stuck on the SAMSUNG logo and did not initiated. I was using the StockRomLite v1.3.RC1 my bootloader is knox enabled ( my last rom was MK4 something).
I formatted, re installed the rom, installed another rom but in rare occasions that system started just after the boot it hung. Even when I put it to recharge the battery icon did not turn in to green ( indicating that was charging) was grayed without animation.
Today I installed the I9192UBUBMK5_I9192ZTMBMK1_I9192UBUBMK5_HOME.tar.md 5 ( stock rom with knox enabled), and my cell is operational again.
Now I tried to root my device without success, kingo does not recognize it. The modified bootloader, hangs when I install it with message "recovery booting ...".
Well Im very happy that my cell phone is operational again, I will worry to root it only next moth