I had the same thing happen on my last double knit project, where I was holding the yarn in a new way, and the awkwardness somehow translated into stitches where half the V was big and loopy!
I believe it is indeed a tension problem. I'm not certain, but it seems like it's just a matter of getting a firmer hold on the yarn. If you wrap the yarn around your pinky as I show in the basic knitting video, you can shut the pinky against the ring finger to keep the yarn from coming through.
KnittingHelp Queen Bee
"There is a vitality, a life force, an energy, a quickening that is translated through you into action, and because there is only one of you in all of time, this expression is unique. And if you block it, it will never exist through any other medium and it will be lost. The world will not have it. It is not your business to determine how good it is nor how valuable nor how it compares with other expressions. It is your business to keep it yours clearly and directly, to keep the channel open. You do not even have to believe in yourself or your work. You have to keep yourself open and aware to the urges that motivate you. Keep the channel open."
— Martha Graham