Computer hanging because of RAM

Anyone else having this issue.

I have 24 cores HP z800 dual xeons with 48GB of RAM
The light build tries to use it all and i had to reduce the number of light to make it finish computing at all. Then when I did the lightbuild , it completed and suddenly my RAM usage went to 47.2GB of the 48GB and my computer hung. It took 16 hours of computing and I have to force restart my system.
I have no lighting results to show for all 16 hours of computing time and have to start from scratch.

This is only happening for me in the 4.16 build and the 4.13 build works fineā€¦