Pipelines UI fails to load list of branches

Issue

The Pipelines UI does not load a list of branches from a remote repository upon clicking the "Start job" button. 

Resolution

Switch the repository source to Acquia Git repository, then back to the external repository. Steps to switch repositories:

1. On the Acquia Cloud overview page, click on the Pipelines menu.
2. At the upper right, click on More Links, then View Application Info.
3. Once on the application info page, click on Configure.
4. Once on the configure Pipelines page, click on Configure under the desired repository you wish to use

To finish, repeat the steps and select the original repository.

Cause

Although an infrequent occurrence, Pipelines can sometimes lose the connection to an external git repository.