.html.erb files commonly used in Rails don't allow breakpoints to be attached
This is similar to #54 and can be worked around by setting the Debug: Allow Breakpoints Everywhere preference. The referenced issue shows that .rb.erb files work by default, so something is being more specific than just the final extension.
This shows the default, without the Debug: Allow Breakpoints Everywhere preference.
After setting, the breakpoints can be added.
I'm not so happy with the global setting, but it is a workaround for now for .html.erb files. It would be great to get this fixed though.