Random missing albums in library when adding new music

Hi everyone, my name is Emanuele and I’m new to the forum.
I use Volumio 2.599 on a Raspberry PI 3B+ with an HIFI card DiGi + Digital Sound Card I2S connected with a coaxial cable to a Marantz amplifier.
For the music storage I have a 4 TB WD Elements (with an external power supply) connected via USB and formatted in exFAT.
The first time I put my music on the hard disk I had no problems. I found all the albums I put on the HDD in the Volumio Library interface.
I had problems, instead, when I tried to add new music on the HDD. Every time I try to upload new albums, in addition to the first upload, I don’t see the new albums at all, or I only see a few of them. And the music missing are totally random: if I try to delete and re-add the new albums, maybe I see some of them who wasn’t there in the previous upload and others that were there before and now are missing.
I also tried to format the hard disk and add all the music again from scratch: I keep seeing all the albums of the first upload, while I see only a few of the new ones.
I also tried to reset Volumio to factory settings, but nothing, same problem.
What do you think cause this and how can I solve it?
Thank you

Hi ema82, I’ve only got about 1500 albums and I’ll add a few every could of days. I used to see this issue but I’m getting it a lot less. This is how I do it, I’m finding that having cover. jpg is more consistent for displaying album art than having a mix of embedded, Folder.jpg and cover.jpg. the other thing I’m aware of is the amount of RAM: there only so much a album art that can be displayed at a time. Lastly, anytime I add a few albums I prefer to rescan rather than update. This helped a lot for me. BTW, I also check my music with tagscanner taking care to avoid the troublesome ’ various artists’ tag.

Thanks crumpeldoor,
I forgot to answer this topic, sorry.
In my case, the problem was related to the presence of special characters (like #) in folder names.