Formulas are nan values in Pandas/Openpyxl

Question

When I am inserting formulas using openpyxl in an excel like such:

#multiple rows
#execution hit on both sides?
from openpyxl import load_workbook
wb = load_workbook(filename = 'flat_user_data.xlsx')
ws = wb.active
for i in ws.iter_rows(min_row=10, max_row= 10799):
    i = i[0].row
    ws[f"N{i}"] = f'=IF(COUNTIFS(A{i-1}:A{i+1},A{i},D{i-1}:D{i+1},D{i},M{i-1}:M{i+1},True)>1,IF(COUNTIFS(A{i-1}:A{i+1},A{i},D{i-1}:D{i+1},D{i},M{i-1}:M{i+1},True)=2,True,"INVESTIGATE"),False)'
wb.save('flat_user_data.xlsx')

When I load the subsequent df I get for these rows only NaN values.. However when I open the excel file and save it these values become the

Is there a way to open the excel file, read the contents via code so that this does not need to happen manually?

Would love to hear your thoughts! Please help