Today I applied the F6 BIOS update to the GIGABYTE GA-AB350M-Gaming 3 motherboard.
This update set my 3200mhz RAM down to 2133mhz and blocked any manual overrides. Even in advanced settings mode. I have gone back to version F5. This version doesn’t still have the boot repeat issue but only happens sometimes.
Back to the drawing board guys!
24/09/2017 update
Applied newly released F7a update and the issue still exists.
Gigabyte’s response:
Please revert and keep the F5 BIOS if this version is work with XMP. For DDR XMP performance on AM4 platform, it is more related to AMD AGESA code (APL code) support and CPU capability.