Usually a '+' icon expands the node on the current page or the '-' icon collapses the node but in this case, nothing happens.
These are new icons implemented in version 13 and this is how the icons are implemented.
The '+' (plus), '-' (minus) and ' ' (blank) icons are visual indicators that let the user know if there are items in the folder; they are not meant to be functional actions for expand and collapse.
Additional Information: Refer to these bugs for further details CLRT-65313 and CLRT-67255.
After review of the mentioned CLRTs above, it was indicated that this is working as design.