I've got my udoo x86 ultra loaded at 100% on all 4 cores 24/7. I've noticed that the temperature of all 4 cores was around 80C (that's the throttling limit I've set up in bios). Turns out that the fans were not spinning at full speed + sometimes turning off, even though the temperature limits I've set for the fans were the lowest (so they would kick in at 100% as soon as possible). I've had to disconnect the fans from the motherboard and connect them directly to the 12v supply to get rid of the problem. Now my CPUs are nice and cold at 65C.
What bios/uefi version are you running? In the latest version 1.0.4 there was some error with fans solved.
I really don't care much now, since the problem is solved for me. I'll try to take a look at the bios next time i disconnect the system. (This is a remote installation).