Unless you're using a WL liner from Chambers or made by them, you may have an aftermarket WL liner knockoff. They are out there. Jim Chambers told me his liners use a slightly smaller than 1/16" (.055" maybe, I forgot) vent hole and he told me he always opens them to a full 1/16".
I first noticed the knock-offs when I built a rifle and used the hole same size. After the first shot it fouled, and when my pick would not fit (very small, 1/32" maybe) I became concerned enough to contact Chambers where I found out the Knock-offs. I only get my WL Liners directly from Chambers now.