When a view is empty, it disappear from the Folder's tab. It is then impossible to know if a folder has Build Pipeline views defined or not. The only way to know is to look at the config.xml that contains obsolete views configuration.
A common scenario for which it could happen is if the Initial Job is moved. For example:
1. I create a simple view "TestView" at Jenkins root 00-view-config-before-move.png
2. I show up in the main page 03-view-config-after-move.xml
3. I move the initial Job "testJob" under the folder "TestFolder". The view disappear: 02-view-tab-after-move.png
4. I check the configuration of the view at $JENKINS_URL/view/TestView/config.xml. See 03-view-config-after-move.xml
Hiding the tab seems wrong as this is the only way to know there is a view configured at a specific level. At least Administrator or user with "View/Configure" privilege should have the right to see those.
An "empty" view in the code is treated as a non permitted view: https://github.com/jenkinsci/build-pipeline-plugin/blob/build-pipeline-plugin-1.5.8/src/main/java/au/com/centrumsystems/hudson/plugin/buildpipeline/BuildPipelineView.java#L772-L774.