Chosen Solution
I broke the glass on my 6s and had it replaced by a third party (not Apple) and sometime later I started losing cellular connection almost every day. This could be fixed by doing a hard restart, but it would re-occur, giving the message “invalid sim”. I took it to the Apple Store and they instantly recognized that it had a third party glass. They put a new sim card in it and everything looked ok, A few hours later however I got the same sim car fail message. I took it back to the Apple Store and they said that I needed to buy a new phone since mine was out of warranty. My question is: can it indeed not be fixed?
My concern here is that whatever impact caused the glass to break may have caused some issues internally. For example, antenna interconnects damaged or partially disconnected. It could also be issues with the logic board itself or perhaps some water or humidity got in via the cracked glass. If your comfortable opening your device, you could follow this guide to see if everything looks okay. Otherwise, I highly recommend you have this looked at by an independent repair shop. Apple will not help you with this kind of problem.
