SUMMARY:

    Dolphin (or the tags.so slave) fails when displaying a "tags" folder when you create a file with a name that includes the tag.

    Affects "hierarchical" tags; in this example the tag "parenttag/mytag" when a file mytag.jpg is created and tagged with "parenttag"

STEPS TO REPRODUCE:

    Create a file:

        image.jpg 

    and assign a tag "parenttag/mytag" to it.

    Confirm that you can see the file in the "tags" folder:

        Dolphin tags:/parenttag/mytag 

    Then create a file:

        mytag.jpg

    and assign "parenttag" to it. Check the "tags" folder again:

        Dolphin tags:/parenttag/mytag 

OBSERVED RESULTS:

    You get a failure:

    Could not enter folder tags:/parenttag/mytag 

EXPECTED RESULTS:

    You see the tagged image.jpg file listed

SOFTWARE/OS VERSIONS:

    Dolphin 20.03.90
    Baloosearch/Balooctl 5.69.0
    from Neon Testing 

    KDE Plasma 5.18.4
    KDE Frameworks 5.69.0
    Qt 5.14.1 

ADDITIONAL INFORMATION:

    Confirming that the tags are created:

        $ getfattr -dR .

        # file: mytag.jpg
        user.xdg.tags="parenttag"

        # file: image.jpg
        user.xdg.tags="parenttag/mytag" 

    and that baloosearch can find the files:

        $ baloosearch //?query=tags:parenttag
        /home/test/Pictures/image.jpg
        /home/test/Pictures/mytag.jpg

        $ baloosearch //?query=tags:parenttag/mytag
        /home/test/Pictures/image.jpg

        $ baloosearch //?query=tags:mytag
        /home/test/Pictures/image.jpg 

    So, as Baloosearch works, it's not a baloo issue :-)

    You can have many files tagged with "parenttag/mytag" and still get the: 

        Could not enter folder tags:/parenttag/mytag 

    message.

    You also get the failure if the "mytag" appears _within_ the filename, for example "name-mytag.jpg"

    Behaviour also seen in

        Fedora 31 (Dolphin 19.12.1, Plasma 5.17.5, Framework 5.67.0)
        fedora 30 (Dolphin 19.08.3, Framework 5.64.0)