When upgrading Discourse using the git pull and ./launcher rebuild app commands, the branch that will be upgraded depends on the branch specified in the app.yml file. By default, a custom install of Discourse uses the tests-passed branch, not the beta or stable branch. To verify the current branch, users can check their app.yml file or run the command cd /var/discourse && git branch to check the discourse_docker branch, or /var/discourse/launcher enter app followed by git branch to check the Discourse branch, as noted by david and martinduparc.