In a category view, the list of files is hidden. If we inspect the page and uncheck "visibility: hidden;" for class "jd_content_wrapper" the list of files appears and we can download files. This happens even with a public file in a public category in a public menu item.
We do have a menu item for "list all categories".

Is this a layout, css or settings issue?
Default layout for Downloads is "Standard Files Layout with Checkboxes v3.9"

Thank you

Found the problem.
At some point we had added custom css into the Joomla template that hid the file display, so we just commented it out.

.jd_content_wrapper {
 /*   visibility: hidden;
  height:1px;*/
}