If you would have looked on the next page on this forum you would have found this;*https://rog.asus.com/forum/showthread.php?92032-Asus-Strix-Z270i-Issues-Red-CPU-LED - 6 page thread about it the issue. Nothing wrong with your PC, this is an issue with Asus BIOS, which they need to fix. But they stopped replying in the thread so i dont know if it ever will be fixed...
Same problem here and i was also using the switch on the back of the PSU. Fixed the problem by keeping the computer on the mains after shutting down the PC. Never happened again.