Floating groups have to be direct children of the page, as far as I’m aware, you cannot have a floating group be inside a reuseable element (somehow you’ve circumvented the error that we usually get for that). Second, I think you have to set yourself up to have two main groups in the REU itself:
- Group
- OTHER group, overflow-y: scroll,
with all of your content groups inside.
Apply the overflow-y: scroll to the Group 2 element instead of the Floating group.
Should work.