Date conversion adds one microsecond

I'm converting date from string but for some strange reason it sometimes add one microsecond in the timestamp field:

logstash 8.1.3

String field: 2022-06-16T13:44:04.615

Logstash code:
date {
match => [ "fluent_time", "yyyy-MM-dd'T'HH:mm:ss.SSSZ" ]
target => "@timestamp"
}

Result: 2022-06-16 15:44:04.616

Has anyone seen anything like this?