Gym Deadlift Day 2 of 2

Wore my black Old School Gym jockstrap to the gym under grey sweatpants for deadlifts today, photos taken at home later. Finally started on my 5/3/1 lifting program spreadsheet again after calibrating my lifts (deadlift, squat, bench press, military press /overhead press) the last couple weeks. It's been entirely too many years. Shirt lifted up showing the jock waistband just a little in back. Jock showed the front as well when hanging from the pullup bar for some spinal decompression. Had to do a progressive bridge hold and release as well on the floor to get it to ease up. Seems to do fine the next day usually, muscles and attachment points can be tender though. Why is that lower back so mad at me?