does not work with my configuration

I'm using checkcites v2.5 and I discovered that in my case it does not list unused refs.

I have a multiple (with inclusions) files book and a single .bib file, I generate the .bcf then I run checkcites obtaining a list of 2349 unused items... but my .bib contains only 2146 items! (I do not have duplicate keys, checked with jabref)

Anyway I random checked some of them and I can confirm that checkcites lists both unused and used references, e.g.:

...
=> trentini2020cittadinanza
...

but in the .bcf I have:

...
<bcf:citekey order="2" intorder="1">trentini2020cittadinanza</bcf:citekey>
...

How can I help in tracking down this issue?

Thanks