Glad you sorted it out. It’s worth checking your file tags for any inconsistencies in the album name (upper case / lower case / etc.) between tracks and, especially, between discs. I’ve noticed with dbPowerAmp that sometimes different discs in a multi-disc set have different titles. Sometimes, the title even has CD1 etc. added to it. If that happens, Roon might think that it’s a different album.
Similarly, check the disc number and track number tags.
This is one of the deficiencies of only doing disc based tagging because the TOC discid used to lookup the disc only knows about that disc, it does not understand the concept of multi-disc albums. Whereas if you tag your songs against a database such as MusicBrainz or Discogs the metadata should be consistent over all the discs in the album and you should get more consistent results.
I manually compared and edited the ID tags to make sure there were no discrepancies. And even then Roon still thought track 10 was its own album. I would love to know exactly how Roon uses metadata (and which metadata) to process multidisc albums.