Instapot slowcooker

Anyone use their instapot’s slow-cooker setting with success? Mine NEVER gets my stuff done. I wanted to do 2 pork shoulders yesterday so I could freeze some. I put 1 in my crockpot on low for 8 hours & it was fall off the bone perfect. I knew my instapot cooked a little lower temp so I did medium & expected it’d take a little longer. At 10 hrs still not close. So I moved it to high for 2 more. Still not close. I was ready for bed so I was like screw it, I’m just gonna turn it on low & let it go over night 8 more hours. This morning, still not done?!? Wtf? Is mine broken? Am I doing something wrong? Or is that setting just crappy & I should stop trying?