Joseph, I use kid3 to check tags on my digital files, if you have kid3 or something similar maybe check that files tags against the other files. Kid3 is free by the way.
Thank you for the recommendation Andy. I’m surprised that there isn’t a way to add a missing track to a disk in Roon - especially considering that they are all from the same media.
Maybe there is, I don’t think Roon can write to the files though? Simplest thing is to load them into something like kid3 and check. You will see the album tag and that is most likely what is incorrect, sometimes just a simple spelling mistake.
Lots of software like Roon, itunes use different databases etc to sort and collate material.
Likely a stray tag in that file. A disc number tag, a compilation tag, a total discs or total tracks tag, etc. just something minor,but different from other track tags. I use mp3tag for all my tag editing.