Ruby on Rails and Javascript confirm popups in Safari 12

In my Rails apps I have a lot of links like this one:

link_to "Destroy", project_path, :method => :delete, :data => { :confirm => "Are you sure?" }

The confirm data attribute used to trigger a Javascript popup (and still does in most browsers).

In Safari 12 these popups no longer seem to work, however.

Instead of the actual popup I get the spinning pinwheel (An error message would have been helpful here, Apple!). No errors are reported in my browser console or Rails logs either.

How can this be fixed?

P.S.: My Rails version is 5.1.4

from Ruby on Rails and Javascript confirm popups in Safari 12