If I am not mistaken that is the address of the statistics server Mattermost uses to collect information about it self and to also warn you about security updates.
That message means that for whatever reason your server was unable to reach the domain in that IP address, perhaps your DNS is failing or not properly configure.
If you wish to disable those messages you can do so by changing these 2 settings
false but you will lose the ability to report and receive reports from mattermost.
For Security Alerts (see link) and for Error and Diagnostics Reporting (see link)