openpyxl generating corrupted workbook

I'm getting some data from MongoDB and sending it to Excel. I'm using openpyxl but some workbooks show the following error when I open them:

  

"we found some problem with some content in excel ...".

Could anyone help me?

Code:

ws = wb.activeclient = pymongo.MongoClient("...")
db = client['...']
collection = db['...']
r = 2
for doc in collection.find({'is_timeline_valid': True}):
   for dic in doc['timeline']['datas']:
     if 'pedido' in dic['tramite'].lower():
       ws.cell(row = r, column = 1).value =doc['id_process_unformatted']
       ws.cell(row = r, column = 2).value = dic['data']
       ws.cell(row = r, column = 3).value = dic['tramite']
       wb.save('pedido.xlsx')
       print('*****************************')
       print(dic['tramite'])
       r += 1