After grouping a bunch of visualizations, there would be a white outline box when hovering over it. It is especially obvious in a darker theme.
This is actually still happening, but grey when there is a white background. It happens when the user is interacting with a visual, such as clicking on a row in a table.
Looks really awful when you have nested grouping as you then are getting multiple lines depending on how many clicks there are on the same visual!! v-qiuyu-msft this clearly wasn't followed up...