BIOS 1402 Memory Training Bug - B850-A - ASUS Confirms "Known Bug" But No Fix

[hypewala]

ASUS Support has confirmed BIOS 1402 has a "known bug" affecting 4-DIMM memory configurations on B850 boards, but provided no timeline for a fix. I'm creating this thread to collect affected users and push for an urgent resolution.

THE PROBLEM:
After updating to BIOS 1402 (December 2025), my 128GB (4x32GB) DDR5-6400 system is locked at 3600MHz. All attempts to enable DOCP/XMP result in DRAM LED and boot failure.

MY SYSTEM:
- Motherboard: ROG STRIX B850-A GAMING WIFI
- BIOS: 1402 (updated from 1066)
- CPU: Ryzen 9 9950X
- RAM: 128GB Corsair Vengeance DDR5-6400 CL32 (4x32GB)
- Previous status: Worked fine on BIOS 1066

TROUBLESHOOTING COMPLETED:
- Multiple CMOS clears
- All DIMMs tested individually - all work perfectly
- 2-DIMM configuration works at 6400MHz (proves hardware is fine)
- Manual voltage tuning attempted
- Tried speeds from 6400 down to 5200MHz - all fail
- Only 3600MHz boots with 4 DIMMs

ASUS SUPPORT RESPONSE:
Support acknowledged this is a "KNOWN BUG" but only suggested generic troubleshooting and told me to "contact local support." No timeline for fix, no beta BIOS offered, no escalation to engineering. After calling technical support, I was told the only option is to send my motherboard in on my dime for them to fix the issue. Why would a software issue require me to ship my motherboard in?

THE CRITICAL ISSUE:
BIOS 1402 states "This BIOS version cannot be rolled back to previous versions" - we are STUCK with broken memory performance until ASUS releases a fix.

WHAT WE NEED FROM ASUS:
1. Timeline for BIOS fix
2. Beta BIOS for testing
3. Rollback solution or RMA process for affected boards

I am hoping the more users who report this, the faster ASUS will prioritize a fix. 

@asus@Jiaszzz_ROG@Silent_Scone- Please escalate this to the BIOS engineering team ASAP.

[Vynra]

You can't just wait for a Bios update release? They literally say they are aware of the bug.

If you rush a bios update then something else might be broken or unstable.

They need time to test these things to make sure the problem is actually fixed and works correctly.

Be patient or roll back your bios.

[hypewala]

The issue was that chat acknowledged the issue, but calling into support did not. Also, last few bios updates did not actually fix the issue. Beyond that, there was no roll back option. 

[Rudi1]

Who uses four sticks of RAM with an AMD DDR5? It's a known issue; you just need to do some research before making a mistake like that. Anyway, there are ways to get them to boot and run at 6400MHz by modifying voltages and adjusting BIOS settings. Besides, with a B850 motherboard, you can't expect much. Look in specialized forums. I have two 64MHz sticks with an X870E-E motherboard, a 9950X3D, and an Aurus Master 5090, and everything works perfectly.

[hypewala]

I was okay to not get 6400 with 4 sticks, but I did not expect to be locked to 3600. I've manually tweaked voltages and tried to get 6000, 5600, etc. and nothing but 3600 will get to Windows. Yes, 2 sticks works, that's not what I am trying to achieve.