Let me tell you my journey how I got slot 1 unavailable intermittently: (1) Add sticky tape on the SIM card. It worked, then not anymore. Until too much pressure causing damage to the Flex Cable. (2) Bought a new flex cable. It seems to work. But, on the same day the problem happens again. (3) Used other SIM card which is thicker (the same card with I used to have when having the phone the first time). Still undetected. (4) I’m almost certain, this is an OS issue. I’m going to use a custom ROM.