X370 Gaming X new bios problem

Specs
x370 Gaming X
R7 1700
32GB DDR4
GTX 1070

I know its kinda gamble when I flashed bios from 5.2 to 5.4, and then bamm..... then I get what I deserve XD!

The problem is with new bios that is it takes around 15-20 minutes just to get inside windows, same with if I wanna get into BIOS; I press del, 10 minutes later bios screen appear.

What I'm trying to do is downgrade the bios to 5.2 again, but it always show invalid file.

So I'm kinda stuck with 20 minutes loading now

Is there is anyway to revert to older bios, or I have to wait for new bios?
BTW I can still RMA my mobo since it's still under warranty.

Just an update, I went to Asrock Service Centre and they told me have several similar case with customer flashing to the latest bios. It seems that latest bios kinda buggy and might not work very well in some case, and told me to wait for new bios update.

Done some testing and here's what I found for my problem:
BIOS 5.2 -> Runs fine
-NVME drives on M_! slot
-NVME drives on M_2 slot
-HDD drives on SATA slot
With BIOS 5.4 -> the loading becomes really long.

-Clearing CMOS and do fresh install windows still have same issue.

-I did try installing 2nd NVME on PCI-E adapter in case bad M_2 slot, but the issue still persist.

-But if I remove the NVME on M_2 slot, the problem goes away albeit there
still bit delay.

-Installing M.2 SATA drives is also fine.

-The issue only appear when I try installing 2nd NVME drives, whether on M_2 slot or using PCI-E adapter.

-They should capitalize this info ---> * User will not able to flash previous BIOS once upgrading to this BIOS version.

Save the headache, DO NOT update to latest bios.