You are getting the error:
bin/rails:6: warning: already initialized constant APP_PATH
when you are trying to start the local webserver with rails s.
That happens when are using the bootstrap rails gem as in:
gem 'anjlab-bootstrap-rails', require: 'bootstrap_rails'
It is important that the bootstap rails uses in the require is used with a dash and NOT an underscore.
So when you write the the gem as follows:
gem 'anjlab-bootstrap-rails', require: 'bootstrap-rails'
and restart your server you should no longer have the error message.