Hi @tetafro,
It looks like there might be an issue with GitLab's gitlab-ctl reconfigure not correctly setting the password in our config. After running a gitlab-ctl reconfigure, can you look at /var/opt/gitlab/mattermost/config.json and see if the SMTP password (and other settings) are being set correctly under EmailSettings?
If it does look like it's being set correctly, can you then set the password from the System Console and look at config.json again. Notice any differences?