We have an Error in one of our views like this:

Call to a member function getSettings() on null

This is thrown as an Error which extends Throwable. The error handling in Smarty only catches Exception for cleaning the output buffer:
https://github.com/smarty-php/smarty/blob/master/libs/sysplugins/smarty_internal_templatebase.php#L249

This messes up our error template output. I think you should catch Throwable on this point.