With 8GB installed in each of 4 RAM DIMM slots A1, B1, C1, D1, the CPU only used 24GB (not using DIMM in slot B1). CPU-Z shows that the 8GB is in B1. I have tried two different motherboards, and swapped the positions of the DIMM to eliminate the memory or motherboard as the problem.
The motherboards were ASUS X299 Mark I and the MSI X299 Pro.
The memory is G.SKILL TridentZ Series 32GB (4 x 8GB) DDR4-3600.
I would greatly appeciate any input.
Some other information that might be helpful. I replaced the i9-10980xe processor with an i9-10920x on the MSI motherboard and it had the same problem (i.e. not likely a processor problem). I then changed the memory from the G.Skill to Hyperx (HX432C16PB3AK4/32)
and then the i9-10920x detected and used all 32GB of memory. I thought "problem solved", but then I reinstalled my i9-10980xe processor and I'm back to 24GB used (slot B1 is not being used).
However, I have found that by overriding the DRAM frequency to 1000 or 1200 MHz from the default 2400 MHz in the BIOS, all 32GB of DRAM is now being used. For obvious reasons, I would like to use the memory at the maximum possible speed supported by the processor (overclocking is not required).