Not sure but I think your phone has “long screw disease”. Basically that’s when you put in the wrong screw in one of the holes in the Wi-Fi/cellular antennas and broke it. It’s a very common thing with iPhones, so I think that’s the culprit.

You will probably need to open up the iPad (you can find a guide here for your iPad) and then remove the power button. Reinstall the power button and it shouldn’t be stuck anymore.