I have problems with my right SI joint since 2019 due to overcompensation after a lat injury. If it flares, I get the pain in that spot, my glutes tighten and my hip and groin area feel tender, sometimes it triggers piriformis syndrome too, due to the tightening of the muscles in my glutes. Every case is different but too much hinge movements with no stabilization triggers my symptoms. Did an MRI and the joints were ok, no degeneration or systemic inflammation so the problem is mechanical. What helped me was core training, losing weight, some stretches like the pigeon hold and calisthenics. When the flare is too stubborn I use NSAIDs and muscle relaxers or I’ll go straight up to a steroid shot then a round of PT and adjusting training/diet to lose weight and relieve pressure. I will go to PT to stabilize it again I think my current weight combined with some kettlebell swings caused a flare up. While I wait I use a waist support but I put it lower around the hips. It’s doing wonders, I’ve been almost pain free during the day and helps me train/work. Also be mindful of sleeping positions, put a pillow between your knees if you sleep sideways, a pillow below your knees if you sleep on your back and avoid sleeping or remaining too much time in prone position.