Check if you have rescue from routing error in your routes.rb
Something like this:
match '*unmatched', to: 'application#route_not_found', via: :all
That prevents active storage path from accessing your stored image in S3, hence the broken image.
I had the same issue and it turned out I put the Upload link outside of the data-uppy="photo[image] div containter.
Make sure you look into the form file in the source code.
that works up until you have more than one component. Then it'll complain rails-ujs is already loaded.
My work around is to add
import Rails from "rails-ujs"
in each script/component.
This is still problematic with Rails 6.0.0rc1