OP, my shooter, a franken luger, had a similar problem when I acquired it about 8 years ago. I worked on it and eventually got it to behave better. I wish I could recall what I did exactly, but I did do some light filing/polishing particularly on the side plate. I think.
One of the gifts of owning a mixed parts Luger is that you get the joy of learning how to fit missmatching parts and then you get to brag about your gunsmithing skills. I am a level three Bubba
Keep us posted on your journey.