Answer:
See explanation below.
Step-by-step explanation:
When RAM size changes unexpectedly it is usually the actual RAM circuit cards, the memory modules. There can be anywhere from one to eight on most work-stations though there may be more. The first thing that a technician might swap out is the actual RAM modules.
Another thing to rule out is the Operating System, the OS. The technician can boot in safe mode to see if the RAM is still 8GB lower.
Once these have been ruled out, then the technician can consider items that are more difficult to change out. One is the Motherboard, which might be causing the problem. The other item that might be failing is the CPU itself. It might have lost the ability to access all of the RAM.
Hope this helps! Have an Awesome Day!! :-)