According to the information provided the issue you are experiencing could be related to the memory controller on the system. Please let us know the model number for the processor on build B and the BIOS version to provide further troubleshooting assistance. Also check the power supply and ensure it is sufficient for the configuration you are looking for.
I recommend you to update the BIOS on your motherboard. There are around 10 newest versions.
Please follow the instructions bellow:
Try to install at least 2 BIOS versions before flashing the latest version 2209.
Thank you. When you say "Try to install at least 2 BIOS versions before flashing the latest version 2209." Does it matter which ones? Should I go for the oldest 2?
Not sure what I'm trying to achieve here by not choosing 2209? I also want to make this 3rd gen capable (IRO my first post on Feb 23).
Jonathan, you can try installing BIOS version 1979 and 2111 using the 2nd gen processor.
Then update to version 2161 since this version fixed some memory issues.
Once you flash these BIOS, you may want to install the 3rd gen processor to verify if the board is now capable to use it.
If you continue having the same behavior, feel free to contact your local Intel support group for assistance on replacing your product: http://www.intel.com/p/en_US/support/contactsupport?group=processor