E.M Pulinx:

May I let  this EXT led blink regularly without any danger then ,or is it better to fix that ?

It's probably better to fix it, because you otherwise never know if it's important.

E.M Pulinx:

How to unroute AES 1/2 and AES 3/4 ?

Probably easiest to select them one at a time, and turn the knob clockwise until you see "