I fixed the problem (2018-4-29)
(on my local Macbook Pro with localhost:3000)
I download discourse codebase again with
git clone https://github.com/discourse/discourse.git original_discourse
and then
bundle exec rake db:migrate
rails s
Now User Preferences Page is ok
I am not quite sure what’s the problem with the other discourse folder I have.
It could cause by theme or plugin that I install. maybe.
Anyway, now problem gone
— Update —
I think sidekiq is part of the problem, I didn’t run sidekiq at my local machine, and got 404
after I run sidekiq the 404 problem gone