If you are planning to turn on airplane mode on your iPhone 7 to save some battery or using it on a plane, you will find that signal could be lost once you turn off the airplane mode.
Some users have reported that restart the phone might be a fix and some of them have to go to Apple store to exchange for a new unit.
It seems that early adopters of any kind of device would have suffered some sort of bugs in the past till the company figure it out and provide a software update or some sort to fix the problem. However in this case, only a few users only had this problem which is the same as the hissgate some people are experiencing.
However is best to return your unit to Apple for a new one or wait for a possible software update.