Unfortunately this is pretty common. While I haven't been denied to any lounges before, I know the lounges essentially have a hierarchy when it gets busy. Priority Pass users are sadly at the bottom of that hierarchy and will be restricted access first due to capacity control when there is high demand. I love my PP, but I am aware of the risk. Fortunately, most of the airports I usually travel to have multiple lounges to choose from, and I haven't been turned away so far.