I have noticed on two Plone 5.1 sites that we experience a condition occasionally where the contents of a folder will show as empty, even if there is content present in those folders. This seems to happen if we have a url that has a repeating "word" at the beginning of its path.
For example https://somesite.com/plone/plone-five.
In the above example, if I remove the word plone from plone-five in the short name of the folder (plone-five in this case), the contents are displayed as expected.
I have tested this condition without front end webservers (nginx and apache).