If phpinfo() is disabled and debug is enabled, it throws this error

[phpBB Debug] PHP Notice: in file [ROOT]/includes/acp/acp_php_info.php on line 55: Undefined offset: 0

It is better on 3.1 because rest of the page is displayed, but I think it should be solved.

Solution:
open includes/acp/acp_php_info.php

Find
if (empty($phpinfo) || empty($output))

Replace with
if (empty($phpinfo) || empty($output) || empty($output[1][0]))