This is by design. The agent bubbles you click in a grouped queue belong to Table View only, so Dual View shows the whole queue again. To see one agent's tickets in Dual View, group the queue in the navigation panel instead.
Why the selection applies in Table View only
When you group a queue by agent in Table View, you can click an agent bubble to show only that agent's tickets. Dual View has no way to show or clear these bubbles.
The selection used to carry over into Dual View. That could leave the queue looking empty, with nothing on screen to explain it or undo it. The selection now applies in Table View only.
When you switch back to Table View, the agent you picked is applied again.
See one agent's tickets in Dual View
In the navigation panel, hover over the queue.
Open the queue's menu and group it by Agent.
The queue splits into a sub-queue for each agent. Click a sub-queue to show only that agent's tickets.
The sub-queue works in both Dual View and Table View.