Hi, Yes I understand what you mean, if the metal part designed to keep the ceramic mouthpiece in place doesn't slide that's cause there is probably some resin and it appears the cold resin to act like glue... So I recommand you to try again right after a session or just heat up the device with the top lid on (but with the silicone screen holder removed), the heat will help you to dislodge the clip. You have to use 2 tools, one maybe a pen, with the bottom of the pen you apply pressure on the clip center and, with the other hand you dislodge the clip sliding it back with a pointy tool inserted in the tiny hole.
Hope that helps, let me know....