I read your code and there is no such logic to read only 65,000 records. And the modules you are using also does not restrict the records. There is no problem in the code. So, I did a little research about this and found that 1 sheet in excel can hold only 65,000 records. Possibly, you have records in different sheets and those are not getting converted. To read records from different sheets, you will have to parse through the sheets. You can refer to the following code to do it:
import pandas as pd
df = pd.DataFrame()
xlfname = 'Productivity Report.xlsx'
xl = pd.ExcelFile(xlfname)
for sheet in xl.sheet_names:
df_tmp = xl.parse(sheet)
df = df.append(df_tmp, ignore_index=True,sort=False)
csvfile = 'sample.csv'