Merge branch 'patch-254' into 'master'

DeadlineExceeded troubleshooting scenario

See merge request gitlab-org/gitlab!44985

doc/user/project/repository/repository_mirroring.md

@@ -577,3 +577,7 @@ Should an error occur during a push, GitLab will display an "Error" highlight fo
 ### 13:Received RST_STREAM with error code 2 with GitHub
 
 If you receive an "13:Received RST_STREAM with error code 2" while mirroring to a GitHub repository, your GitHub settings might be set to block pushes that expose your email address used in commits. Either set your email address on GitHub to be public, or disable the [Block command line pushes that expose my email](https://github.com/settings/emails) setting.
+
+### 4:Deadline Exceeded
+
+When upgrading to GitLab 11.11.8 or newer, a change in how usernames are represented means that you may need to update your mirroring username and password to ensure that `%40` characters are replaced with `@`.