Troubleshooting Collection annoyance

[troubledMan]

I discovered recently that my Voyager was stuck indexing at the 123th book of a total of some 170. As I read here, I did a reset to factory settings and that solved the issue. But now I’ve found that a particular collection does not summarise the books that contains: the books are there but under the collection’s name I read “No elements” (in Home Screen, list view). It happens that this collection groups all my books that I haven’t bought in the Amazon’s kindle store and USB-transferred. Other collections created for books bought from Amazon do show normally the number of elements in them.
If I get information about the collection, I can read in the pop up window, under the collection’s name, something that puzzles me a lot: “In the Cloud: 13” “Downloaded: 13”. How is possible that if those books were USB transferred?
I keep my Voyager in Plane mode all the time and transfer all my books via USB, except, of course, when I have to register it in order to use collections.
I would like to know if this is something normal using the last update (5.13.3), or better, if there is something I can do to solve this annoyance.
Thank you in advance and, please, excuse me if this is a silly question (or it has been answered previously).