I have just installed ArcPro 2.2 and I have found a quirk with Pro when using SDE data. By default when I open the Labeling Properties dialog box it has the SDE schema name.SDE feature class in brackets which fails when I verify the expression so no labels appear. I need to delete the default value and double-click on a field name from the fields drop-down list. These are extra steps which are unnecessary if Pro formatted the SDE feature class properly by default.
Now if I perform the same process on a file gdb feature class and I enable Labeling it works by default without having to fix the expression in the Labeling Properties dialog box.