When the NOPRINT option is specified on a PROC UNIVARIATE statement and BY-processing is done, the procedure will incorrectly issue:

Note: BY-line has been truncated at least once.

if the LINESIZE= system option is set such that one or more of the BY-lines would be truncated if they were printed.

If you are also specifying an OUTPUT statement, the OUT= data is created correctly with no truncation of the BY values.

The Note can be ignored, or to try and avoid the Note, you can specify the maximum linesize and reset it after the procedure. For example:

options linesize=max;
proc univariate noprint;
  var x;
  by byvar;
  output out=out mean=meanx;
run;
options linesize=80;