gmt --version: 6.2.0
Mac M1 12.0.1
I meet this bug Linux system too. other gmt6 versions have the same bug:
gmt begin
gmt figure a pdf A1c
gmt sac -JX10c/1.1c -R-2.23517e-07/20/-4.80721e-06/4.30574e-06 bug.sac
gmt end show
The red arrow points out the bug, which is a short line

the sac file is in the zip.
bug.sac.zip
gmt --version: 6.2.0
Mac M1 12.0.1
I meet this bug Linux system too. other gmt6 versions have the same bug:
The red arrow points out the bug, which is a short line

the sac file is in the zip.
bug.sac.zip