в файле moodle\lib\dml\mysqli_native_moodle_database.php найти READ COMMITTED и заменил на REPEATABLE READ
что то не работает(
// Set transactions isolation level to REPEATABLE_READ
// prevents dirty reads when using transactions +
// is the default isolation level of MSSQL
// Requires database to run with REPEATABLE_READ_SNAPSHOT ON
$sql = "SET TRANSACTION ISOLATION LEVEL REPEATABLE READ";