These exception types are being ignored as part of the default configuration of that gem. See line 25 here: https://github.com/smartinez87/exception_notification/blob/master/lib/exception_notifier.rb which currently reads:
@@ignored_exceptions = %w{ActiveRecord::RecordNotFound AbstractController::ActionNotFound ActionController::RoutingError ActionController::UnknownFormat}
You can override this behavior in your environment file (i.e. development.rb, etc).
Example to notify on ALL errors:
config.middleware.use ExceptionNotifier,
ignore_exceptions: []
Example to add RuntimeError to the default ignore list:
config.middleware.use ExceptionNotifier,
ignore_exceptions: ExceptionNotifier.default_ignore_exceptions + [RuntimeError]