Steps to reproduce:

1. Open frontend, get the message:
   
2. "let the game begin" (c) John Kramer

Result:
https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/ui/include/classes/db/DB.php#133

Expected:

Source code has better error description than the user error:

		/*
		 * Detect either the query is executable at all? If query is valid and schema is correct but query still cannot
		 * be executed, then there is a good chance that previous transaction has left row level lock unreleased or it
		 * is still running. In such a case execution must be stopped, otherwise it will call self::refreshIds method.
		 */

Add additional logging which can print database error in PHP error log, for example, add before https://git.zabbix.com/projects/ZBX/repos/zabbix/browse/ui/include/classes/db/DB.php#132:

error_log('mysqli_error: '.mysqli_error($DB['DB']));

For the end user it will be helpful to see:

• failed query - since it gives information to work with
• information why the query was failed - locks, timeouts