Why would the command SUMTYPE,PRIN affect a single result set?
It is more pronounced in cases of large strain.
When SUMTYPE,PRIN is set the component stresses are zero. This
behavior could affect nodal averaging.
With the default SUMTYPE,COMP you are averaging the component stresses
at a node and then computing SEQV from the average component stresses.
With SUMTYPE,PRIN you are averaging the equivalent stresses directly because
the component stresses aren't available.
I created a two element test model that shows SUMTYPE,COMP and PRIN
give the same results when one element is selected at a time, but
when both are selected the value at the common node is a little higher
with SUMTYPE,PRIN [attached to Incident 359224.]