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
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