Tried bumping to Twig 2.0 locally, getting a Twig_Error_Runtime: Accessing Twig_Template attributes is forbidden. in ROOT/templates/tracker/issues.index.twig:47 error message. From a quick search, this is usually related to macros, but in this particular case the error line is using our translation filter ({{ 'Status'|_ }} is the exact issue). Trying to add a filter named translate or using the functions doesn't help matters.

So, something in our setup is causing Twig to bug out. Whether we've hit a core bug with them or it's an issue on our end is to be determined.