Ok, thanks to all.
I had to make it by craigmcg solution, because when the problem happens, I have tried first to rebuild totally the library, so I have deleted the libraries directories... with the backup too!
Any error has its lesson itself inside, so for the next time...
Anyway, I have done it like this, but I will check and rename manually later, because they take the full name, with album name.
Thanks again, and I hope that it's not a bug that will reproduce. Maybe better if I keep my 13 version...
Half hour later:
Put back the 13, because when trying to correct, he makes it again! but on ALL the files this time!
So I cancelled all, and put back the old version, and when rebuilding library, I just see now that not all the files are corrupted. Most part is right! Can't understand and don't wont to!