Most people pull the lat pulldown bar too low, rounding their shoulders and shifting work to the front. Stop just below your chin and drive your elbows down toward your hips instead of back. This keeps your shoulders safe and actually activates your back muscles.
Stop doing this on your lat pulldowns. It's ruining your gains. Most people try to come all the way down to try to get a full range of motion, but you shouldn't do this because when you get to the bottom, you round your shoulder forward and this takes the pressure off of your back and puts it on the front of your shoulder. And this is why most people don't feel their back muscles and just end up hurting their shoulder. So what I want you to do instead is to bring the bar down until it's right below your chin level. And one more bonus tip: when you pull the bar down, don't think your elbows are going back, and instead think your elbows are going down to the top of your hips. It'll be easier to maintain correct form, and you'll feel your back muscles a lot more.
