No solution to my original post, however...
I work mostly with ArcMap still, so I have no idea if this will also apply in ArcGIS Pro, but I've had phantom labels appear for features whose values aren't included in a category-based symbology schema. So, if you've removed a certain value from the feature's symbology (and unchecked the <all other values> class), make sure to also apply that omission to the labeling SQL query, too. This is because an omitted symbology class is essentially still on the map as an "invisible" feature; if you want to fully hide a feature from the map, including its labels, using a Definition Query would accomplish this.
Hope that helps!