Lightroom Classic CC (7.1 release).
I have the left-most column of the library module (the Navigator, Catalog, Folders, Collections and Publish Services) set to "Solo Mode" so only one section is open at a time. Often (not every time) when I start Lightroom Classic CC and open the "Folders" dropdown it only opens a few pixels - enough to show a list of maybe five, five-and-a-half folders in all. There is no scroll bar so I cannot access the rest of the list. If I close then re-open the "Folders" section using the dropdown, it works properly.
Bug needs to be fixed.