I'm sharing my story to, for what it's worht
I live in Sweden and I also have this problem with my brand new (as of june 2017) Galaxy s7.
It started after I had my phone on service through my carrier (is that what it's called? My net provider?/where I also bought the phone) for a broken display, when it came back, I noticed two connected kinds of problems:
1. I had problems with making calls and sending texts, aswell as recieving calls.
2. I had problems connecting to the mobile data net, lacking 3g and 4g connection too often, resulting in slow internet, and not being able to access the internet at all sometimes. This seems worse when I commuting, btw.
My Carrier sent me a new sim, had me do a factory reset, and I still had the problem. So I sent it back to my carrier to repair it again. They changed the entire circuit/mother board, sort of everything except the battery and shell, they said. BUT, the problem presists! The report said they found no problem with the phone but they did not mention any testing before the changing of the circuit/mother board. They only subjected it to standard tests after having replaced the circuit/motherboard.
While having my phone on repair, I was given a replacement phone, a galaxy a4 or a5. It worked like a charm, no problems, even when commuting.
Now I do not know what to do, I would have them send my another phone, I'll even take a cheaper one, as long as it works!

We will see what they come up when I ask to have it checked again. I figure I'll will use it/test it for one week before reporting the issue again, though.
My suspicion at this point is that this is a software issue since they replaced the circuit/motherboard on my phone and the issue presists.