Here is minimal testcase I have come up with

stmt = mysql_stmt_init(ma);

mariadb_stmt_execute_direct(stmt, "SELECT 1,2", strlen("SELECT 1,2"));
mysql_stmt_store_result(stmt);
mysql_stmt_free_result(stmt);
mysql_stmt_reset(stmt);

mariadb_stmt_execute_direct(stmt, "SELECT 1,2", strlen("SELECT 1,2"));
mysql_stmt_store_result(stmt);
mysql_stmt_free_result(stmt);

mysql_real_query(ma, "drop table if exists t_count", strlen("drop table if exists t_count"));

mysql_real_query(ma, "create table t_count (a int)", strlen("create table t_count (a int)"));

mysql_stmt_close(stmt);

The error occurs on 2nd mysql_real_query. Moving mysql_stmt_close(stmt); above them changes nothing. Removing one of mariadb_stmt_execute_direct eliminates error.
Lowered priority - closing, instead of resetting stmt between two mariadb_stmt_execute_direct calls eliminates bug. And closing is the right thing to do.