Multi-branch pipelines with branch names using non-standard characters will return 404 errors from the REST API for certain endpoints.

Example:
Here is the URL for the "jenkins-design-language" project's branches:
https://ci.blueocean.io/blue/rest/organizations/jenkins/pipelines/jenkins-design-language/branches/

Any branches with special characters return a URL with the branch name in URL-encoded format (expected).

The "feature/JENKINS-35912" branch returns a 404:
https://ci.blueocean.io/blue/rest/organizations/jenkins/pipelines/jenkins-design-language/branches/feature%2FJENKINS-35912/

Accessing the same URL with the branch name double-encoded works okay:
https://ci.blueocean.io/blue/rest/organizations/jenkins/pipelines/jenkins-design-language/branches/feature%252FJENKINS-35912/

Ideally the branch names would be single-encoded. I think it's fair to expect the end user or application shouldn't have to URL encode the URL in order to use it, unless this is a HATEOS convention I'm not familiar with.