I found this article on Racer.com by Marshall Pruett, prior to this year's Indy 500 and it goes into some detail about the issues the drivers are facing with the universal aero-kit. Since that article was written, the issues the drivers face are still there.
https://racer.com/2018/05/18/indy-ae...moving-target/
IndyCar is going to have to re-evaluate the UAK and in particular the underwing, which generates the majority of the car's downforce, before next season, or 2019 will be more of the same.