Welcome to PhotoStructure @Cristiano_Magnani ! I’m the author.
What antivirus are you using? Unfortunately, I can only support Microsoft Windows Defender: see this for more details.
A big update is coming which includes two things that should make debugging this issue much easier: “health checks,” one of which verifies that ffmpeg is behaving as expected and is a supported version, as well as “sync reports”, which will tell us exactly why a given file is not being imported.