Okay not your simple "bad form" back pain. I'm fine while I'm doing the exercise. Keeping the weight over my heels not "breaking" at the waist. Controlled motion up and down. I don't feel anything pain while doing the exercise it's when I rack the weight and come out from under the bar. I get the pain sensation like my lower spine is decompressing. I don't have pain the day after but my lower back does feel tired? Is this just my core needs more strength or what?
BTW I did 3X8 365 was planning on four sets but my back was too tired / sore for the last set only completed 5 reps then racked it. So it's not super heavy weights either.