slow query log without specific sql command

[Harrison Jhon]

mysql 5.6.35
ubuntu 14.03

this is a slave mysql server.recently,I've seen a lot slow query records like this:
# administrator command: Prepare;
# User@Host: gcenter[gcenter] @ [192.168.168.102] Id: 2769933693
# Schema: gcenter Last_errno: 0 Killed: 0
# Query_time: 10.219548 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 Rows_affected: 0
# Bytes_sent: 1704
use gcenter;
SET timestamp=1490604733;

or this:
# administrator command: Prepare;
# User@Host: acenter[acenter] @ [192.168.168.106] Id: 2769933435
# Schema: appcenter Last_errno: 0 Killed: 0
# Query_time: 11.359057 Lock_time: 0.000000 Rows_sent: 0 Rows_examined: 0 Rows_affected: 0
# Bytes_sent: 1112
SET timestamp=1490604733;

I can't find out why, Does the master-slave synchronization cause this problem? cos I have'nt seen this kind records in the master slow log.
and how to solve this problem?
really appreciate for your help!!!