Rspec System Test passes when run individually, fails when run with entire suite

Cannot be sure without a lot more information. It would be best if you can create and publish a minimum complete verifiable example.

Based on the information given, I would guess that the test that fails when run with the other tests is not properly isolated. The other examples are changing the state of the application, causing this test to fail. So look at your before and after hooks and make sure you are setting config.use_transactional_fixtures = true in rails_helper.rb

If it is possible for there to be a delay between the time #del_one_event is clicked and .swal2-actions appears, then change

within('.swal2-actions') { click_button('Yes') }

to

find('.swal2-actions').click_button('Yes')

If none of those fix the problem, you might have an issue with browser caching, but that is even harder to debug.