There may be easier ways to fix this but this is how I’ve done it in the past:
Open Music and go to Songs view. Right Click on the first song choose Get Info and review each item in the Detail and Sorting tabs. Continue through the entire list. Something will be different on one or more of the fields in each of the “split” songs. That is what has divided the CD.
Once all fields in all songs are the same the CD should go back together. Copy & Past will be your friend in accomplishing this.
I had the same problem. In some cases I could not find anything different in the Get Info panel for the songs, so I changed the info in both albums to something else entirely, then when all the songs were together, I adjust the info to the correct data.
Thank you very much @WayneG. I got back to this today and followed your guidance and looked for any anomalies. The one glaring difference I found were in the artist fields. It is modern choral classical cd and just seeing the composer’s name is sufficient for us.
Once I changed them all, all tracks got reunited except 2!!! I have looked and looked and cannot see anything in each field which would cause those to be separated.
I found the album in the finder and all tracks are listed today - even 14 and 15 which are the “rogue” tracks. See images. I am now coming back around asking for more help!
Since two tracks from the same CD are frequently identical, except for the track(song) title, I’d copy and paste the info from each field (except the song title) from “problem track 1” to “problem track 2”.
Seems like even an extra space in one field is enough to cause a problem.