Astrolabe's labeling is a hierarchical process. All cells start as "Root", then they're labeled according to compartments of increasing resolution. For example, "Root" -> "T Cell", "CD4+ T Cell" -> "CD4+ T Cell (Treg)". If a cell doesn't fit any of the labels in its level, it becomes "Unassigned". One of the labels out of "Root" is "CM-", which means that the cell is negative for all canonical markers (usually CD3, CD19, CD56, and CD14 or CD33).
"Root_unassigned" means that Astrolabe could not label the cell as anything, not even CM-. This usually means that the cell is a doublet (if it's CD3+ CD19+ then it's not a T Cell, not a B Cell, but it's not negative for CD3/19 either).
"CM-_unassigned" means that Astrolabe decided the cell is not any major compartments, but then could not label it within the CM- level.