GL-HOOK-ERR: or Giltab:not displayed on Gitlab UI

Hi all,
I have created a simple hook in “pre-receive.d” on a gitaly server

#!/bin/sh
echo "msg to STDOUT";1>&2
echo "GitLab: prefixed msg to STDERR";
echo "GitLab: prefixed msg to STDOUT\nwith a second line";
echo "GitLab:a second safe message with no whitespace separation";
echo "not prefixed by, but containing GitLab:";

echo "msg to STDOUT";1>&2
echo "GL-HOOK-ERR: prefixed msg to STDERR";
echo "GL-HOOK-ERR: prefixed msg to STDOUT\nwith a second line";
echo "GL-HOOK-ERR:a second safe message with no whitespace separation";
echo "not prefixed by, but containing GL-HOOK-ERR:";

exit 1

but when I tried an action on gitlab ui (example a push) I receive a blank error section

If I try to launch the push via cli, the messages are displayed

git checkout -b a; git push -u origin a; git push -u origin --delete a;
[...]
[...]
remote: msg to STDOUT
remote: GitLab: prefixed msg to STDERR
remote: GitLab: prefixed msg to STDOUT
remote: with a second line
remote: GitLab:a second safe message with no whitespace separation
remote: not prefixed by, but containing GitLab:
remote: msg to STDOUT
remote: GL-HOOK-ERR: prefixed msg to STDERR
remote: GL-HOOK-ERR: prefixed msg to STDOUT
remote: with a second line
remote: GL-HOOK-ERR:a second safe message with no whitespace separation
remote: not prefixed by, but containing GL-HOOK-ERR:
To 'http://xxxxx/yyyy/zzz.git'
 ! [remote rejected] a (pre-receive hook declined)
error: failed to push some refs to 'http://xxxxx/yyyy/zzz.git'

I also tried to test the hook with only GL-HOOK-ERR: or only GitLab: with no success.
I also tried to test the hook with and without the “1>&2” redirect

Where am I wrong?

Thank you
M.

Gitlab Version: 14.6.1 installed via OMNIBUS
OS: Ubuntu 20.04 LTS