The magnetic plate indeed warps, not due to heat though but the material on it warping. I saw that on both the i3 Mega as well as a Prusa MK4S with PETG and ABS. Printing big solid objects close to a corner would cause the corner to be lifted up, as the warping of the object is often times stronger than the magnetic plates. Probably gives you an idea of how much force a glass plate has to withstand, especially with badly warping materials like ABS. You can counter this issue with some strong clamps. Doesn’t happen on most prints anyway, only on really large and solid ones. The magnetic adhesion in the center is strong enough for anything.