All Touchscreen Quality no good

Even with the best quality glass it is hit and miss to get one that works correctly every time.....I have done over 400 successful ipad screen replacements and it really is luck of the draw whether the new screen works properly. No matter how carefully you do the work sometimes the new screen's connectors simply do not plug in crisply and hence the screen doesnt work. I've tried 5 different brands of screens inc IFIXIT and they all do it at some point.....Anyone got any useful info on this phenomenon ?