It's super replicate-able with the first example on https://elastic.github.io/eui/#/tabular-content/data-grid-virtualization where you see a flash of it adding the body class then it gets instantly removed again. https://user-images.githubusercontent.com/549577/130854234-c2857bdd-7e4d-45ef-bba7-7369a004582a.mp4
It's super replicate-able with the first example on https://elastic.github.io/eui/#/tabular-content/data-grid-virtualization where you see a flash of it adding the body class then it gets instantly removed again.
Screen.Recording.2021-08-25.at.03.36.51.PM.mp4