Hi, I had the same problem with my Xperia X after it falls down. Didn't solved after factory reset…. I lose the front camera, the back camera and flask at the same time. I supposed something in the motherboard and I finally decided to change Brand. I had a Sony xperia T, xperia Z, xperia Z1 and Xperia X. Sony has Great devices, but made to have a short life. And I'm very careful with my devices…
So, If anyone will solve this problem please share the solution