Native query length

Hi, i have a problem wih Metabase v0.30.1. on OpenJDK and Debian 9.
My database is MySql, and when I insert a native query longer than 256 characters metabase remains locked on the message doing science. Debug side displays the message “DEBUG metabase.middleware :: POST / api / dataset 200 (1 s) (5 DB calls) Jetty threads: 8/50 (3 busy, 5 idle, 0 queued)”. If the length of the query is less than 256 characters, it is executed correctly by metabase and the result is displayed.
On any Mysql client, the query over 256 characters is executed correctly.