After our last composer update, rollbar/rollbar-laravel was upgraded from 2.3.0 to 2.4.0. Immediately following, Rollbar began reporting critical errors pertaining to RollbarServiceProvider.php
Here's the log entry:
production.ERROR: exception 'Symfony\\Component\\Debug\\Exception\\FatalErrorException' with message 'Call to a member function getStatus() on null' in /var/app/current/vendor/rollbar/rollbar-laravel/src/RollbarServiceProvider.php:50\nStack trace:\n#0 {main}
Forcing composer.json to 2.3.0 using "rollbar/rollbar-laravel": "2.3.0" and running composer update resolves the issue.

For reference we're running Laravel Framework version 5.2.45 and PHP 5.6.24