Hi @SuziQ,
Can you switch to your last working backup and perform the upgrade again, using the steps provided below:
cd /tmp
wget https://releases.mattermost.com/5.25.2/mattermost-5.25.2-linux-amd64.tar.gz
tar -xzf mattermost*.gz
cp -R /opt/mattermost/config/* /tmp/mattermost/config/
sudo su
mv /opt/mattermost/data /tmp/mattermost/data
rsync -au /opt/mattermost/plugins/ /tmp/mattermost/plugins
rsync -au /opt/mattermost/client/plugins/ /tmp/mattermost/client/plugins
systemctl stop mattermost
mv /opt/mattermost /opt/old.mattermost
mv /tmp/mattermost /opt/mattermost
chown -R mattermost:mattermost /opt/mattermost
(If you have setup TLS) sudo setcap cap_net_bind_service=+ep ./bin/mattermost
systemctl start mattermost
Confirm Mattermost is working
rm /tmp/mattermost*.gz
rm -rf /opt/old.mattermost/
If the issue persists, provide the output of journalctl -u mattermost and any errors in the /opt/mattermost/logs/mattermost.log file