My microwave is in the process of dying the exact same way as my previous one. The latches on the door slowly wear grooves into the plastic they run over to latch. At first the door starts sticking and won't close and open properly. Then it stops latching altogether and becomes unusable. Both microwaves were purchased from Costco, I don't remember if they're the same brand.

The fact that this has happened on two microwaves in less than 6 years makes me consider that it's planned obsolescence. Of course I will try to repair the latches myself, but this could easily have been avoided had they used metal or even a harder plastic. I'm sure that people in charge of these decisions are informed about how long the products are expected to last.