Hidden items in album (that should not be hidden)

Hi KDE Discuss community!
I hope my topic can be of some help to others; here is my problem:

As said in the title I have an issue with hidden items.
Selecting some of my albums, which are indicated with a number in parenthesis after the name (so I know that DigiKam know that something is there) I can see no content in the miniatures view.
For sure the first thing I’ve did was to double check the filter section, but no filter is active.
Digikam itself, in the lower left corner of the window reads something like:

No item selected (0 items) - One hidden item

(Note1: it may be one or other numbers, depending on the album;
Note2: I’m translating this form my localized version, so words may not be exactly the same)

I’ve tried to check every config parameter in menus without finding something addressing this situation.
Another attempt I’ve made was to copy one of those “hidden” files in albums with normal behaviour, but they remain hidden even in the new location (when the rest of the album is normally visible).

I’ve run out of ideas, so…
Does someone have any hint on how to understand what’s wrong?

Thanks in advance!

Oh, I’m using DigiKam 7.5.0 on Kubuntu 22.04