Steps to reproduce

Upgraded my Gemfile to 6.0.0.beta3 and bundle update ran smoothly
Running rails app:update however stumbles with this error

ArgumentError: Invalid route name, already in use: 'root'

# routes.rb
root to: 'system/frontpage#index', constraints: lambda { |req| req.session[:user_id].nil? }
root to: 'welcome#index', constraints: lambda { |req| req.session[:user_id].present? }

Expected behavior:

This should not cause an error I believe since this is a valid configuration and I haven't gotten this error before on previous versions.

System configuration

Rails version:
6.0.0.beta3