[RedDevil]

It is actually pretty simple.
These LEDs and many other electronic components are made in the cheapest possible way; that is, good enough to pass quality control and initial testing.
Little consideration is given to the stresses the repeated heating up and cooling down cause over time.
Hairline cracks appear in the soldered connections and the component fails.

When you put 2 metal objects very close together in a microwave, you'll see a spark between them. The hairline cracks are bridged, re-solder themselves and the component works again.

The problem is that other gaps can be bridged too - if they are not supposed to they'll fail. The PN layer in diodes, transistors and ICs is vulnerable.
Also anything metal quickly heats up by itself - and LEDs are notoriously heat sensitive.

So there's a minefield of possible problems.
But if you have a failed component that you can't or won't repair otherwise, good ventilation and it's not your microwave anyway, why not give it a try?

You can better step it up very gradually indeed or use a buffer like a glass of salted water (to aid conductivity).