The Pentium G4400 is compatible with the board according to board support page here. OP please verify that this is indeed your motherboard:
www.asus.com
Same page also says that Pentium G4400 is compatible with all revisions of the board and it's been validated since BIOS 0801. The first ever BIOS for the board seems to be this version 0801 so the board should not have compatibility issues with the CPU.
I think the error 4F is "DXE IPL is started" so maybe a memory issue. Is that "Kingston Hyper X 16gb 3200Mhz DDR4" a single stick of RAM? Is is installed in the corresct slot? Slot A2 (2nd from CPU)? If it's two sticks (2x8GB) they should be in A2 and B2 (2nd and 4th from CPU)
If it's just the one stick have you tried it in slot any of the other slots to see if that makes a change? in B2 maybe?
Can you perhaps borrow some other RAM (lower clock) from somebody and test on the board?
I too would at this stage guess the BIOS chip might be faulty. Although you said you have been able to flash the latest BIOS version to it ? Changing the CMOS battery of the motherboard is a very good point too.
A bent CPU pin, said above, can be an issue too.