Ok, so, it works like this:
“Gapless playback” is a codec feature that is enable on LAME MP3 files since many years back, and most other modern codecs (like at least AAC and ALAC). It has to be written as tags to the files at the time of encoding them. On playback, it’s up to the player and decoding process to read those gapless tags and present the audio accordingly. There’s no option to enable, it either works or it doesn’t. Volumio, using MPD and modern, standard codecs, supports gapless playback out of the box.
However, if you rip your own CDs, you need to make sure you do it with the gapless option enabled (if one exists) and with a codec that supports it. When the files are ripped, you need to populate them with metadata, like ID3 tags, so that any player knows which track is the first, second, and so on. It also needs to match the album name and artist/album artist/composer tags, so they play together.
Volumio has all it needs to play a full album back-to-back gaplessly, as do many modern audio players, but you have to make sure your files are prepared that way.
I think, either your files are wrong somehow, or don’t contain the gapless data necessary for the player to know when to end and begin the next track, or you’ve found some bug. Either way, I think this subforum is the wrong place, since what you’re asking for is already supported.