With the fix for http://tracker.phpbb.com/browse/PHPBB3-11158

// Do not display signature panel if not authed to do so

if (!$auth->acl_get('u_sig'))

{

  $module->set_display('profile', 'signature', false);

}

was removed from ucp.php

This code however caused to skip the module, rather then displaying the error message, when it is the first module to display: https://github.com/phpbb/phpbb3/pull/607#discussion_r2285193

There is a huge different thing in this and the signature part must be readded!

if the first module is not accessible, the line

$module->set_display('profile', 'profile_info', false);

will cause the next module to display, instead of trigger_error, which will cause inaccessible submodules of the same parent!

To reproduce on this branch, with my code still in place, remove your profile and signature permission and try to navigate to the "Edit account settings" from the index.php. You wont be able to, as it displayes

You are not authorised to define a signature.

So you see, the profile module is skipped, but the signature module isn't and therefor throws the error.