The independent scroll bar for Row-Level Security in Power BI Service no longer scrolls. There used to be two scroll bars, one for the entire window and one for the Row-Level Security portion. Without the independent scrollbar, it is very time consuming and difficult to modify Row-Level Security in Power BI Service. Additionaly, when in Row-Level Security, there is nothing that indicates which report you are editing security on. Adding the dataset name would be very helpful to this page.
For the scroll bar in the security page about Power BI Service, have submited this issue internal to confirm(ICM: 315324139), would update here as soon as possible if there is any progress about it.
About adding the dataset name in the security page, currently it is by design in Power BI Service as far as I know because we always click the dataset name to configure RLS for it in details. Perhaps you can submit the requirement to ideas and add your comments there to make this feature coming sooner: https://ideas.powerbi.com/forums/265200-power-bi-ideas
It is a place for customers provide feedback about Microsoft Office products . What’s more, if a feedback is high voted there by other customers, it will be promising that Microsoft Product Team will take it into consideration when designing the next version in the future.