Adding hostname to failure log helps to trace the problem
(if it depends particular cluster client)

pkgsrc@makoto 09:44:52/230328(/export/CHROOT)% diff -u usr/pkg_bulk/libexec/pbulk/pkg-build{.orig,}
--- usr/pkg_bulk/libexec/pbulk/pkg-build.orig   2023-03-28 09:32:04.696316980 +0900
+++ usr/pkg_bulk/libexec/pbulk/pkg-build        2023-03-28 09:44:52.142836039 +0900
@@ -146,6 +146,7 @@
 rm -f ${bulklog}/${pkgname}/*
 
 touch ${bulklog}/${pkgname}/work.log
+echo 'hostname: ' `hostname`      >> ${bulklog}/${pkgname}/work.log
 /usr/sbin/chown ${unprivileged_user} ${bulklog}/${pkgname}/work.log
 
 pkg_add_normal() {