If capybara/rspec is required before rspec/rails in your spec_helper.rb file, then you will be unable to use the capyabara ‘visit` method in a request spec unless it is nested inside a second describe block. See the lone request spec for a reproduction.
Interestingly, it seems unnecessary to require capybara/rspec at all. If I remvoe that entirely, the tests pass. They also pass if I require rspec/rails first.