Mothur crashes when using too many cores

I have a server with 32 cores and 48 Gb RAM to use for my analyses and when I run mothur commands with 16 processes or more then most of the time mothur crashes. (pre.cluster, classify.seqs and chimera.uchime crashed for me) What may cause this?

The more processors you use, the more memory is required. I suspect mothur is crashing because you are running out of memory.