Failed to parse field with format date_time

Hello,

ailed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [
2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517]
 with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] 
 with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] 
 with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] 
 with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] 
 with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] with format [date_time]failed to parse date field [2021-10-06 14:21:39.517] 
 with format [strict_date_optional_time||epoch_millis]failed to parse date field [2021-10-06 14:21:39.517] with format [strict_date_optional_time||epoch_millis].

To be honest this could be a couple different issues. But the moral of the story is you have a field that can not be parsed because the Date/TIme is not correct format.

Do you have a custom index template?
Did you create a extractor on a INPUT?

With the lack of information given that is about the best I could do for you.
For a better understanding please look here.