Android 6.0 update - System UI not working

I updated my Z5 to Marshmallow 6.0 yesterday. Worst mistake of my life. It locked out my phone and wiped some SD photos (so I couldn't get past the keylock screen - on entering the correct code, it goes black momentarily, thinks about it, then returns to the lock screen on a never ending loop). Clicking any notifications fro the dropdown menu brings up the keylock screen again, and on inputting the correct keycode in, I get the error message 'unfortunately, system UI has stopped working' then it returns to the locked screen again. I can receive calls, emails and texts...but I cannot access them, or send anything. Worth noting that I already did a factory reset (and lost further photos from my sons 5th birthday), which fixed the problem last night...and this morning it return in the same manner as above. About to do a further factory reset, but that's no way to live my life with a 3 month old phone.... Someone please help (And also any help on recovering my SD images would be welcomed!) I have been to x2 O2 stores, with one Guru who couldn't' find a solution. THANKS! Maria