When a segment is created from within a report by dragging a component on the segment area, it is possible to re-use It in another report?

Refer to the exhibit.

Analyzing results from multinational e-commerce, a data analyst realize much of the product view results and orders are being mapped to an ''unspecified'' department name.
What is the probable cause?

Utilizing a segment identifying website traffic from the Unified States, an executive team member from a computer manufacture is viewing a report showing daily computer sales in the United States. In the component rail the executive sees a segment for ''United Kingdom and drags it directly into the dataset to break down a specific dimension. Every attempt return zero activity.

Why would the dataset drop to zero?

Certain links on your website are resulting in a 404 page.
Which dimension should be used to find out pages are affected?

Anomaly detection alerts the analytics team to a spike in product view on a specific views on a specific item. User further investigation the discovers that a remarketing partner is sending illegitimate traffic to the website. Business partners are asking that the analyst team exclude the traffic from both future report and past reports.
How can this request be accomplished?