[JRTJH]

It almost sounds like the door frame is warped along the top. If the magnet will hold a wrench, it's not the magnet that's at fault. Sounds more like the door is pulling away from the magnet (spring action). You might try "tweeking" the top of the door by using a screwdriver inside the frame along the top edge to bend it out a touch to take some of the tension off the door when it's in the open position.

If not that, possibly the vinyl weather stripping is not bending enough to allow the door to fully open???

Otherwise, I'd be out of ideas.