@nedotepa, see how “same length” is the typical bad reason for merge: How is "compilations" a reason to merge?
@Van_de_Bugger, there is unfotrunately no undo/revert.
It’s a tedious manual redo with loss of history.
You have to create a new standalone recording for the most recent added track.
After the creation of this track, badly merged recording should relate to the oldest added track.
You have to add data to it (AcoustID, ISRC, relationships) that you can confirm they should be there.
You have to remove everything from badly merged recording (AcoustID, ISRC, relationships) except those that you can confirm they should be there.