iPod touch 4g camera not working

I have been repairing broken screens for a while now and just had my 3rd ipod touch 4th gen have the camera lock up. I have done tons of research and tried the fixes but it doesn't help. I am considering not doing it anymore because it's too costly replacing people's ipods when it happens....i do sell the "broken" one as a 3rd gen to recoup my money but it's becoming stressful. I wish someone could pin point what is happening.....it must be something getting damaged when you lift the board to put the new digitizer plug in. If I knew what part gets damaged, I may be able to be more careful with that area.

I do believe that the copper foil attaching the midplate doesn't affect anything when it's cut. It's always separated when I do a repair and I still have sucessful repairs.