When the branch name contains a +, e.g. foo+bar, the "Open Blue Ocean" link converts it to a space, e.g. /blue/.../detail/foo bar/1. This causes the browser to encode it as %20 when followed, and Blue Ocean to load a blank page. The link should instead encode it as %2B
Also as pointed out in the similar
JENKINS-40137, Blue Ocean should probably show an error in this situation.