Support for ESR 5.9 has ended: Upgrade to ESR 5.19 for improved security, performance, mobile app compatibility, and user experience
As of April 15, 2020, Mattermost Extended Support Release (ESR) version 5.9 is no longer supported. If any of your servers are not on ESR 5.19 or later, we highly recommend that you upgrade immediately. With our simple upgrade steps, it takes only a few minutes. Mattermost adopts a monthly tick-tock release cycle, with a new version shipping on the 16th of each month.