CI 3 DB LOCKING ISSUE ON SET SESSION sql_mode = REPLACE(REPLACE(REPLACE(REPLACE

If you own your server yourself, just set the same settings in your my.ini file, that way you don't need CodeIgniter to set it for you.
As to why it suddenly hangs... have you updated the server version? If not you really should, not to fix this, but for security.

thanks for your reply 

for that my.ini you mean mysql config right ?

im using AWS so yes i will check on it later

and may i know what this query actually trying to achieve ? 

SET SESSION sql_mode = REPLACE(REPLACE(REPLACE(REPLACE(REPLACE(REPLACE( @@sql_mode, "STRICT_ALL_TABLES,", ""), ",STRICT_ALL_TABLES", ""), "STRICT_ALL_TABLES", ""), "STRICT_TRANS_TABLES,", ""), ",STRICT_TRANS_TABLES", ""), "STRICT_TRANS_TABLES", "")

and why CI core suddenly executing that query ? 

i didn't even made any change on my script before this but that query suddenly appear on my mysql monitor and make my application become very slow