In the last photo it looks burned. I can't see well, you should investigate it further, but there are 2 small circular spots that look like burn + crack in the PCB. I looked for more photos and can't see any of those circular spots at the same place.
Worth noting that the motherboard never gave me funny issues, and overclock the CPU pretty well. Could it be something relating to the color coating of the motherboard that might crack over time? On that spot I gave a clean with isopropyl alcohol, due to some tiny thermal paste drop about one year ago (I think normal administration).
Update: I talked to Asus customer service, and all they could say was a simple "coloration and cracking of the protective layer due to normal use over an high temperature working load". I told them, if it was safe to be like that and they simply answered me that I need to contact the shop where I bought the motherboard.
I'll keep up to date guys, and thank for your answer Mr.Wolf.
I opened an RMA procedure at the shop, so that this issue could be investigate even further. The CPU cooler spacer have always been tightened by hand precisesly to avoid this sort of damage. But within a closer inspection it's not the problem, as if the spacer would be overtighten the crack should start from the spacer hole, which apparently is not in this case.
I'll keep you up to date and thank you again for your interest Mr.Wolf.