iPh5 with instable signal after display assembly+batter replacement

Hi guys,

after having replaced the display assembly and battery of my iPhone 5 i have noticed that 3G and LTE signal is instable. I mean in the same place I have full 3G signal and then it switches to Edge.

Is it possible that i have damaged something following iFixit guide? However i don't understand why sometimes everything is fine and sometimes i have such problems.

Thanks.