I have tested the project on iOS and I see the issue you are having. I then created a new project with only Vuforia ARCamera and a cube. This project had the same error so this seems to be an issue with Vuforia.
I had to download Unity 2018.3.9 and update my Vuforia to be able to build your project. Sometimes things break when updating to the latest versions, I know, this sucks. Internally we have started using Unity Hub so we can test out new Unity and Vuforia builds before they are stable enough.
This problem seems to be out of our control, I can only suggest using an older version of Vuforia and / or Unity. We work with Unity 2018.3.0 and Vuforia 8.0.10.