PM Windows 10 64 Bit, V5 Build 19728
I downloaded a zip file of photos from Google Photos.
C:\...\test\Photos (9).zip
After unzipping, into C:\...\test looked like:
Photos (9)                                      File Folder              Today  7:05 PM -------
  20190000-Else                                 File Folder              Today  8:08 PM -------
    20190201_092818.jpg                  324 KB JPEG image               Today  7:01 PM -a-----
    20190201_092820.jpg                  237 KB JPEG image               Today  7:01 PM -a-----
    20190201_092823.jpg                  334 KB JPEG image               Today  7:01 PM -a-----
  20190201-VVKG-XXXX                            File Folder              Today  7:08 PM -------
    20190201_090320.jpg                  352 KB JPEG image               Today  7:01 PM -a-----
    20190201_090325.jpg                  281 KB JPEG image               Today  7:01 PM -a-----
    20190201_090328.jpg                  346 KB JPEG image               Today  7:01 PM -a-----
  20190204-VVKG-Test_2                          File Folder              Today  8:08 PM -------
    20190204_095717.jpg                  215 KB JPEG image               Today  7:01 PM -a-----
    20190204_095719.jpg                  215 KB JPEG image               Today  7:01 PM -a-----
    20190204_095720.jpg                  198 KB JPEG image               Today  7:01 PM -a-----
  20190208-REader                               File Folder              Today  8:08 PM -------
    20190208_093803.jpg                  542 KB JPEG image               Today  7:01 PM -a-----
    20190208_093804.jpg                  492 KB JPEG image               Today  7:01 PM -a-----
    20190208_093849.jpg                  369 KB JPEG image               Today  7:01 PM -a-----
  20190208-VVKG-Type_3                          File Folder              Today  8:09 PM -------
    20190208_103802.jpg                  681 KB JPEG image               Today  7:01 PM -a-----
    20190208_103804.jpg                  615 KB JPEG image               Today  7:01 PM -a-----
    20190208_103813.jpg                  236 KB JPEG image               Today  7:01 PM -a-----
Photos (9).zip                          18.6 MB Compressed (...          Today  6:21 PM -a-----
Using the explorer I opened the five folders in one operation
In this case only 4 folders opened.

After close each folder from the right side, using the X on the folder, I closed the last.
There was one strange folder left

Note the missing folder name and band along the top
This pane is also kind of non-actionable - I can click images, not not the folder 
I can open a new folder from the tree on the left, see it, 

and when I dismiss the new folder, I see the previous mystery folder.
I cannot dismiss the mystery folder without restarting PM
If I rename the base folder from "Photos (9)" to "Photos 9", opening the 5 folders from the explorer still does not work, leaving the "mystery folder" underneath all the others. Or it opens only one. I thought the Parens in the path might trigger the folders, but it looks like a different issue.