Thanks for your reply, sir!
After some trials last night, I found it works the problem happens to those compilation albums, such as sampler, and those album with different artists for different tracks. In fact, I've already set the "album artist" of these compilation album as "Various Artist" and they work well for years in Voyage MPD Linux. So far seems those albums without different artists is fine. And I think the scan is completed.

And interestingly, I also found that, this problem also happens to win & mac desktop version "Cantata 2.3.2" https://github.com/CDrummond/cantata/releases. That's my main and favor mpd desktop client. Also it happens in "Rigelian" v1.4.2 (an iPad MPD app) https://www.rigelian.net/ on my iPad. But Rigelian gives me some insight. Those compilation album are showing as different albums with different Artists. And even worse is, it doesn't work with Snakeoil properly. The Album tab doesn't work with Snakeoil at all.......

But, with android mpd client app "MAFA" https://play.google.com/store/apps/detai...ndroid.mpd . So far this app can show all the files normally. I'm not sure what is happening. Just a layman guess, I doubt it's something about the name used in "album artists".

If you don't mind, would you please tell me how to solve it? Thank you very much. Thank you very much again, Snakeoil.

Best,
Billy