Penyebabnya bisa banyak...
yang terbaik adalah Anda mencoba...menangkap... pengecualian dan memeriksa kesalahan
from pymongo.errors import BulkWriteError
try:
bulk.execute()
except BulkWriteError as bwe:
print(bwe.details)
#you can also take this component and do more analysis
#werrors = bwe.details['writeErrors']
raise