Does Amsterdam have a culture which is in your culture group, but which is neither an accepted culture nor your primary culture? The modifier "Manpower in same Culture Group provinces" does not give manpower in provinces which are accepted or which are your primary culture. There are other modifiers for that.
The manpower in unaccepted same culture group provinces is working correctly:
View attachment 1131720
Though one could argue that the reform could also give "Manpower in Accepted Culture provinces"(manpower_in_accepted_culture_provinces) and "Manpower in Primary Culture provinces"(manpower_in_own_culture_provinces).