MB Works with Gen 1 CPU, but Not Gen 3

I have an X370 Gaming K4 motherboard, with a 1700 CPU. It works fine. I decided to update to a 3600 CPU. I flashed the UEFI to the latest version, which does support the 3600. I reset the BIOS with the 1700 still installed, and reset everything to defaults. I used the computer a couple of days with no issues.

I installed the 3600 today, and it will not work. It powers up, and gets just far enough for the monitor to come on, but will not post. It cycles, over and over. I put the 1700 back in. It works fine. Tried the 3600 again. No luck...

Any ideas what I might be doing wrong???

my x370 taichi also messed about with a similar upgrade

what i found worked
reset defaults with the 1700
shut down
HAVE ONLY 1 STICK OF RAM IN SLOT A2
fit 3600 (or 3800 in my case)
and it boots to bios ...........
save and exit
fit 2nd stick of ram in slot b2
reboot to bios
set xmp
save an exit
and it works again all fine

this happens if i get over zealous with overclocking or it dosnt like a setting , so have to go back to one stick of ram and a bios reset to get the first boot then fit the ram to b2


dont ask me why it will only ever boot 1 stick with a fresh biosflash/reset

but it works try it

I had followed the progression as per the notes, but going back a couple of versions got it working. I was then able to reinstall the latest. Thanks for the help!