Album/artist not found from Volumio on raspberry pi3 model B

hello everyone,
i have a little problem, i noticed that not all the albums on my external hard drive are seen/found by volumio.
i use volumio on raspberry pi3b
95% of the albums on my hard drive are in aiff format, imported and cataloged the same way.
The example I notice now is that for example in the folder " Rod Stewart " where inside I have 3 albums ( each in its own dedicated folder ), Volumio finds only 2.
I have already tried unplugging the hard disk and redoing the search from " source ", and I have already tried the refresh button.
I had previously had a similar thing happen to me with Janis Joplin ( in the hard disk present Janis Joplin folder with one of her greatest hits ), Volumio couldn’t find anything by Janis Joplin at all.
For both cases I solved it by removing the album and replacing it with another ( different ) one

Many thanks in advance
Best regards +++

Check that the tags are consistent and present. MP3Tag is free and handy for that task.