Teeth seem to shift more in Hawley retainers. Is this possible?

Hi, I have Hawley retainers but I feel like my teeth shift _more_ in them than without them. Is this possible? My hypothesis is that the pressure from the retainers + grinding and tongue thrusting on the acrylic is causing them to move and since the Hawley doesn't cover all surfaces of the teeth, they're able to. Some movements I notice include teeth flaring and extrusion.