This issue has been widely reported. I thought I was lucky and had no issues but recently found that not to be the case when I had to reboot my phone literally 9 times during a 400 mile trip.
I've made this same trip about 28 times now and never had to do this with the 6 plus.
So is it a widespread issue? That remains to be seen, but I can confirm that I too have experienced this.
It is interesting to note that when cellular service drops, gps positioning drops as well. I wonder if this is a baseband\modem software issue?