Hi, i copy/paste te solution worked for me (From XDA forum, problems star with a fall)
My sim-cards wouldnt be recognized, sometimes only one of them, sometimes both. Additionally, my fingerprint-sensor wasnt working too. By checking pictures of a disassembled phone I could locate the problem inside. It has a connector on the lower end of the phone, which is for sim and FP-sensor. I can definitely and easily come loose.
Quick and dirty fix for me, was pressing with controlled but quite some force on the lower end of the LED-Rog logo while the phone laying flat on the table. I used my thumb, pushed and restarted the phone to check. Didnt work, pushed a bit harder and restarted again until it worked. The back glass has some flex to it, to make it possible to push the connector back in. Still, be careful to not break it, if you try it yourself.
When I found that solution, I've sent it in on warranty for proper fixing with this Information to ASUS. They replaced allegedly the mainboard. But I actually think, they just fixed the connector in place, because bending the phone to a certain degree "unfixed" it in my case again. I dont know, if its the same issue you have, but if it is, hope it helps everyone.
