I just had this same issue with 1903. Mine is cause by a Samsung 860 EVO as the secondary drive. Remove that and the computer boots. I rolled back to 302 with Winflash and was able to reboot with the EVO drive in. However, upon restarting again it auto updates to 306 on startup.
Thank you very much Narkanin , I had the same issue with a 860 Evo as 2nd HD.
Thanks to your post I was able to reflash 302 after removing the second HD. windows then booted fine from my M.2 SSD
It is a very weird behaviour, with 306, I also was stuck in Asus logo without the opportunity to enter bios.
I do not get an auto update for the 306 Bios, so everything is "back" to normal.
Btw, is there any way to reset Bios when having this problem?