Because on marshmallow "system root" doesn't work anymore i tried myself and when i type "su" on terminal emulator it doesn't work, because to gain access as root you must patch the sepolicy that are located in ramdisk,and when you modify the ramdisk md5 of the kernel get changed, and i think when the bootlader decrypt the cryptohash of kernel and compare that value with the md5 of the kernel(i'm not sure 100% that the verification work like that)and the value mismatch,output that message and a SMC call(into TEE) to set the warranty bit to 1...
Gotcha... ok thanks again for the explanation.
It's not worth worrying about really.
I just thought it might be a simple fix to get rid of that annoying warning every time I boot