IOS 9.1 iPhone 6 dropping network

Hi there,

Does anyone have the same problem?

I have an ios 9.1 iPhone 6 and the phone is losing network constantly during the day. I have noticed that it happens usually when I want to unlock it in order to use it. The phone is losing network suddenly and then comes back after a couple of seconds.

I had no problem when I first purchased the phone (July 2015) but now that is way to much.

The most annoying thing is that when the signal drops down, 1 out of 3 times the 'No Sim Installed' appears and then i have to turn off and on the phone.

I have replaced the sim card (with 3 network UK) and I have reset the network settings. The only thing that they've told me in the apple store was that they can replace the phone as this is something that they can't spot if it doesn't happen at that particular moment.

I don't want to replace the phone because is fairly new but I don't know if I have any other options because it doesn't look like to be a network problem.

Is this something that iPhone 6 have as a problem?