Uncaught ReferenceError - I18n is not defined (after upgrading 1.5 to 1.6)

I run Discourse on my own AWS account and it runs on Ubuntu EC2, ElastiCache Redis, and RDS Postgress.

It ran well when using discourse 1.5 and I upgraded to 1.6.

Before: v1.5.0.beta13b +140
After: 1.6.0.beta1

After upgrading to 1.6 using # launcher rebuild app, the web browser cannot display ant pages. Here is the screenshot of Chrome Developer Tool:

Just fyi, the issue has been resolved after deploying and testing several times. It looks like a temporal issue which may happen one time on a first upgrade.