My filament sensor was burnt  

My filament sensor was burnt

Last night when I was doing a multimaterial print, the loading and unloading of filament failed repeatedly after about 2 hours of printing.

When I touch the filament senosr cover(above the extruder), it was really really hot so I removed it to check.
I found that the undersurface of sensor cover near the laser sensor was molten 😮 , some molten filament stuck there and the filament sensor itself was so hot that it hurt my finger.

Then I checked the LCD panel, it showed that filament sensor was N/A.

So is it that my laser sensor was cooked?

I remember that someone in a facebook group mentioned something similar but at that time I paid no attention and thought it wouldn't happen to me....

Still I don't know why the filament sensor would burn, is it supposed to be disabled by MMU? Even if it was enabled, I don't see why it could be damaged. My MK3 is just over one year, I am afraid the warranty is overdue now 🙁