From what Liam Cunningham is saying in his spoiler-free comments related to filming Season 7, things are “coming to a head” and that’s what is contributing to the tension on the set.
Because Game of Thrones is expected to end at the end of Season 8, the show is currently working to wrap up all of the major plotlines.
Although George R.R. Martin has said the ending will be more bittersweet than devastating, we’re assuming there’s going to be plenty of death and destruction on the way before the final moments of the show.