iTunes 12.8.2.3 on Late 2008 MBP running 10.11.6 (El Capitan). Trying to merge imported discs from a box set into one album.
Previous attempts have sometimes mysteriously subsumed separate discs into a single album, with sections reflecting their original listings (disc 1, disc 2, etc.) in just the way I'd like rather than interlacing tracks into a salad of songs in "perfect" track order but no disc number subheading. But this has usually been when I have cut and pasted the same album title to separate imported discs.
I have explored the Album Info options, post import, to try to better merge in the manner in which I prefer, but a few are stubbornly resisting my custom classification efforts...