Hello,
I've had this Xperia Z3 for about three years. It had a screen replacement twice. Before I always used just a simple "jelly" case (hard to describe, not the one that "closes" like a book).
Anyway, about a few months back I switched to a sturdier phone case - you can "close" it with a clasp, so the screen is covered and the backing is thicker. Anyway, since then I've noticed that my signal strength is getting poor. It's still quite good outside (even though in certain places it disappears randomly); however, when I'm inside a building or something, it goes to "no service" quite often. People also complain that they can't hear me very often.
Anyway, I did a little experiment and removed it from the case completely - the signal strength became much, much better. Has anyone else experienced such an issue? I really don't want to carry my phone around without a case, so I'm not sure what to do. Did anyone have a similar issue and solved it?