Logstash Kafka Input: divided message received


I have a question for Logstash Kafka input.

Here are versions for what I use:
ElasticSearch: 7.3.2
Logstash version: 7.2.1
Kafka version: 2.1.0

Here is input configuration of Logstash:

input {
  kafka {
    bootstrap_servers => "Kafka_SERVER:9092"
    topics => ["TOPIC"]
    codec => "json"
    group_id => "staging"
    consumer_threads => 4
    type => "mysql"

Here is my question:
Sometimes, we receives "partial" message like



ser":"root[root] @ []","host":"","os_user":"","ip":"","db":""}}

Even, no ERROR found in debug mode.
And I cannot find first part of the log (If the log was divided in some reason then we must have all parts) .

I supposed we received JSON format message.

To test configuration, I added this configuration:
fetch_max_bytes => "52428800"
max_partition_fetch_bytes => "104857600"
max_poll_records => "200"

But, it didn't work.
What can I check more to fix this issue?