Windows 10 only using half the installed RAM

Device name DESKTOP-AJD2UQS
Processor AMD Ryzen 7 1800X Eight-Core Processor 4.10 GHz
Installed RAM 64.0 GB (31.9 GB usable)
Device ID
Product ID
System type 64-bit operating system, x64-based processor

Edition Windows 10 Pro
Version 20H2
Installed on ‎2021-‎03-‎15
OS build 19042.631
Experience Windows Feature Experience Pack 120.2212.31.0


My problem is in bold. Windows and the programs in windows can't use all RAM.
I had an older installation of windows 10, version 1909 and it has the same issues as this new install from MS download to a formatted USB drive build version 20H2 on a new SSD.
BIOS shows all 4 sticks of RAM and currently set to XMP profile 1. I've used different BIOS versions and RAM configuration settings with no change, except faster or slower performance.
I've used memtest86 full test (which took ~14 hours to complete!) and zero errors on all 4 sticks of RAM.
CPU-Z detects all RAM with the only difference being two were mfg. 1 week earlier than the other two.
I found some other answers on this and other forums and tried their suggestions to no avail, which include:
The MSConfig -> Boot -> Advanced -> Maximum Memory check box
I've also put all 4 sticks into a gigabyte B550 Aorus Pro with an AMD 3700x with the same result, so it's not the processor, board, or BIOS.
The current system is:
Gigabyte AX-370-Gaming K7 BIOS F4
AMD Ryzen 1800X


- - - Updated - - -

Another post in this forum asked for someone with a similar problem to show a CMD WMIC query.

Ctrl+Alt+Del to open task manager, then the performance tab, then Memory on the left. What does that show?

khx2400c was not seen on the QVL.

For testing purposes please use RAM displayed on the Qualified Vendor List (QVL):
https://download.gigabyte.com/FileLi...-gaming-k7.pdf


There were approximately 14 missed BIOS upgrades.
Upgrade the BIOS to the most up to date non-beta BIOS: F4 > F50d
GA-AX370-Gaming K7 (rev. 1.0) Support | Motherboard - GIGABYTE U.S.A.

NavyLCDR:


zbook: That memory is on the QVL for this motherboard and summit ridge:


Memory part numbers listed in CPU-Z for this memory doesn't match the actual RAM part numbers for some reason. I've highlighted the RAM in the system. It seems like I should have 4 of the %4/64 ones and the %2/32 ones don't support 4 sockets, only two...but I've heard of people putting a lot of mismatched, completely different RAM in their system and they all run but just at the lower speed ones..

I've run BIOS f50d and that didn't change anything, in fact, its loaded on the other BIOS on the same motherboard, I decided to shut off dual BIOS for this install, as a failed boot will swap the BIOS and cause more problems.

Please run:

BSOD - Posting Instructions
How to Upload and Post Screenshots and Files at Ten Forums

Open msconfig > boot > advanced options > post images



Run:

GetMemoryConfiguration.bat - Click here to go to the BSOD batch repository to download and run this batch file.

Tuneup.bat - Click here to go to the BSOD batch repository to download and run this batch file.

As per the screenshot in the OP's post #4, there is 64.0 GB of RAM, of which 32.1 GB is hardware reserved, so Windows can only use the the rest. 64.0 GB − 32.1 GB = 31.9 GB.

Thanks for the rep! It is always appreciated!

Why does the OP's hardware use as much as 32.1 GB? Mine uses only 99.8 MB.