Concrete bahaving really wird since updating

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Hi,
I really don't understand what can be going on, but since I upgraded to 5.6 some very odd things happen .... odd like one page is showing one way one minute and another way after a while ... I just can make any sens of it and not sure what could be going wrong.
Not sure if that could have messed up something but I did change the areas code on page types in order to hardcode the different stacks I was using. So for instance I changed many

<?php
$a = new Area('something');
$a->display($c);
?>

To this format

<?php
$stack = Stack::getByName('something');
$stack->display(something);
?>

Now I did not use the same names as the area names ... could that have messed things up ?

Any help will be appreciated.
Many thanks